hit escape to bring up the clip board map.
right click anywhere on the map and you will see a drop down menu appear.
from this menu you can select to show field elevation.
Your altimeter is reading the altitude above sea level that you are at. The field you are on is 350 ft above sea level.
Just as a sid enote. Are you sure its reading 350 ft and not 3500ft?
field elevations here are generally 0' , 1,000' , 1,500' etc etc.
cheers,
RTR