I'm not sure what you're used to flying but I found pulling my convergence in by about 30% helped me out.
Might help some, but I have mine set @ 350ft the same as I set any other plane with the exception of the B25H and that's out like 600ft I think.
To the original poster, I checked your score to see which 109 you are flying. Looks like the G14 first off that is probably the best 109 to learn in because it turns well but it doesn't shoot 20mm's it shoot's 30mm's. (at least I'm almost certian it does)
I was the same way with 109's oddly enough the first time I ever flew K4 was in the "Der Grosse Schlag" scenario. I ended up killing three P51's and two of them were on the deck in a 2 vs 1 fight. I actually have the film online so I'll post it.
http://www.gametrailers.com/player/usermovies/117694.htmlI laugh at that film now, because I was making all kinds of dumb shots that I'd never do now. I also never HO in the plane but that was my first time in it and both the P51's tried to HO me on a few different passes, so I took the opportunity to return the favor once it presented it's self.

After this I tried to fly the 109 and couldn't hit anything, so call the film above beginners luck if you will. I can't really say what did it for me, but I couldn't kill anything in the 109's for the longest amount of time then one night out of the blue it just kinda came from me. It literally came to me in one sortie, I don't really know what happened but I went from not being able to hit a thing to being able to make kills.
One thing I will say is you need to kill on the snap shots as much as possible. It seems odd but direct six shots in tatter planes are some of the hardest shots to make, simply because you don't have the ammo to "spray and pray" like 90% of the AH plane set, and a dead six profile is kinda small and can be very difficult to hit with a single shot aircraft. It seems odd to say that, because any other aircraft a direct 6 shot is the easiest to make but in 109 tatter plane's its the exact opposite.
I fly the K4 about 90% of the time now and one thing that always annoys me is when people call the K4 a uber plane. That plane is soo far from uber the only advantage it has is a awesome climb rate because it's motor is a powerhouse. Other than the motor it takes a lot of practice and skill to fly because it fly's like a brick. There is no other plane in the game that I have to work the controls so much during a fight. In short flying 109's is all about constant throttle control and flaps. It's not so much about your aim but working to set up the shot.
I'll post a few films that might help you learn how to set up shots..
First one is kinda slow at the start but has some good 1 shot kills in it before I ended up getting gang banged. I did however make them work for my kill, so this film also shows what a K4 can do on the deck..
http://www.wargamerx.com/k4/gangtards.ahfThis second film is pretty slow paced and not how I like to fly, in short it's easy mode. It's actually the sortie after the one above but I stuck to the typical 109 BnZ picktard type kills because I got gang banged the sortie above. This is how 90% of the players in the MA fly 109's and honestly I'm not a fan of this kind of flying but I did have some good shots in here that might help you learn how to set up kills.
http://www.wargamerx.com/k4/6kills.ahfThis is more of the flying I like to do..on the deck in the watermelon especially in these films you see most of my kills don't come from taking direct six shots like you would in any other plane. I'd say 80% of my kills in a K4 are snapshot kills.
http://www.wargamerx.com/k4/k4-vs-5.ahfThis is my favorite kind of fight in a 109 just because it's totally opposite of how most people in 109's fly. There is nothing I like better than upping at a base getting attacked by a CV and fighting on the deck under 3k. Yea have to stay under 3k to avoid puffy and IMO that's where the K4 really shines because it has lots of motor for low alt fighting.
http://www.wargamerx.com/k4/6kills-with-agent.ahfThis one is another on the deck at a CV fight.. kinda boring the first 8 mins or so.. Was just dealing with a bunch of land grabbers and a typical MA pick tard so no real good fights just a lot of defensive flying. Just something to show those that think K4's can't turn.
http://www.wargamerx.com/k4/2-k4sorties-cv-battle.ahfHere is a rare film of me in a G14.. I don't fly it much because it turns too good and screws me up when I go back to the K4. (I did nice pick job on Betty in this one

)
http://www.wargamerx.com/k4/G14.ahfAnyway if you do stay in the 109's don't listen to people that say they can't turn. Once you get your aim down, get it on the deck and in the weeds because that's where the real fun is. Most of the guys that only fly them to BnZ just don't have a clue as to what the planes can really do. In short the K4 is like flying a brick, yea have to use the throttle and flaps and smack it around quite a bit. They aren't a wussy plane you gotta treat them rough like a red headed step child and beat them around a bit.