Biggest problem I've seen is overcorrecting. This is fairly common with beginners. I used to do it all the time. Just make small adjustments on the stick, and you should start to solve the issue. It just takes practice. Of course, you could have a clevise, or steering arm loose, but I would imagine it's probably pilot related. You can practice without the wing on--just practice runs. Be careful, though, not to run it off the end of the runway and tear it up.

When you are ready to do it for real, just ease into the throttle, and let the plane start to lift on it's own. Don't touch the elevator until the plane is ready to fly. It will become light on the wheels, and you'll know it's ready for rotation. Then, rotate it slight nose high, and watch it climb out like a champ!

Something else you might check for is a tight main wheel. Sometimes you get one wheel collar tighter than the other, and the plane will try and do circles around the tight wheel. Make sure both spin freely! Other than that, just practice!