Check your hinge moves freely and that there are no points where it touches the vertical stabiliser. Then look at where you put the control rod on the servo arm and control horn. The horn is the bit that attaches to the elevator, if you have multiple holes the one closest to the plane moves the surface the most, the one furthest away moves it the least. On the servo horn the hole farthest out from the servo moves the control surface the most. Also did you centre the servo first?
You will also want to check that the servo hasn’t peeled the paper off the inside of the fuselage, that has happened to me with the FT board, I now strip the paper off where I am glueing my servos so they stick to the foam directly.
If it’s not a mechanical thing then look at the end points on your transmitter, you can alter those to get more throw too.
A few clear pictures will help people sort out what’s happening.