Hi!
Sounds like you not a club member?!
Could be many reasons to why your plane does not fly like it should.
First set up your radio correctly! That means using 100% trow or more on all channels but throttle.
Do not use any dual rates of differential or expo ...at least not the first flights.

The first thing to check on the plane if it doesn't fly straight is the wing! check for for warp. It's very vital that you have wash-out in the wing (wing tips) . If you have wash-in in the wing , your plane will behave like you tell us, drop a wing, and fly very badly!