[Disregarded9-side]

When shooting two-handed (left hand over right hand), keep left thumb over the right thumb. Left thumb is probably touching the mag release.

If your thumb is that far down, you're grip is far from being "with the times" (if you will). This is more or less how I hold a pistol:

Try to fire using as close to the middle of the pad on the first joint on your trigger finger.

Sounds like you may also want to compare yours to another to see what the mag release spring is like, and perhaps replace it.
Godspeed and good luck, sir!