The next question to ask (if the wing is warped) is one tip twisted up or the other twisted down vs. what the original was?
Guess wrong, the glider may fly straight but have other "less than desirable attributes".
I remember one 2 seat glass trainer that was fine at lower speeds, but the polar nose dived at speed due to the factory wing twist (that helped with stall/spin). Drag went really bad at speed.

Heck, a bad "broken tail boom repair" could have the vertical fin slightly skewed, this can impart a yaw that can show up as you see.
All control surfaces are centered/equal, but the fin is adding yaw.

Has it always been like this, or has it developed over time?