Second video, first 2 engagements...you got a twisty stick or pedals? If so why aren't you using it to help you aim? It looks like you are flying with it uncalibrated or after its shot off.
The first shot...you see him flipping over, you need to flip over with him a neg G shot is hard to hit and you will overshoot...like you did.
Second is just lead....pointing right at a P38 isn't going to get you anything if he is moving....you need to shoot where he is going to be. Look at his nose and draw an imaginary line from it then shoot at where your convergence is going to meet his plane in full force....
Finally, learn to set up easy shots....even in a 1v1 you can set up a high percentage shot...just have to learn it, unfortunately I can teach it but I'm sure TC could help you out there.