One way to find out if it's an airframe issue, or a thrust aligment issue is to loop the plane under power and see if it wants to roll out of the loop, then repeat the process with the engine at idle. If the plane rolls out under power, but tracks straight when at idle, then you have a thrust alignment issue. If the plane rolls out in both conditions, then you have a warp or control surface alignment issue.

I had this problem with my son's NextStar - I had to add a couple of washers under the right side of the engine mount (I need one more washer, but the attach screw is not long enough so I've left it as it is).

Hogflyer