Becase the airplane taxi's straight on the ground has little to do with rudder trim in flight. Nose wheels are seldomly accurately set along with other problems. Generally though this is not the one most have trouble with on first flights, It is either pitch trim (elevator) or roll trim (aileron) that can be exciting on a first flight. Yes if airplane continues to Roll (dip a wing) in one direction you would trim that out on a test flight. If it wanted to dive without holding up elevator you would trim up into the elevator.

Watch TV while holding the Tx and if you are flying mode 11 practice finding both the elevator and aileron trims with your left thumb without looking. Never look at the Tx in flight to find a trim lever.

If you do not already have some flight experiance. Don,t do a test fly yourself, Get help.

John