It can be hard, sometimes, to tell if the problem is too much wing incidence or if it's a thrust line issue.

What I do is take the plane up high, pull back the power, wait for the plane to slow down, then push in to a dive. The idea is to see if the pitch trim changes too much with airspeed with out changing the engine power output.

Compre the results of dive testing to what happens when you increase and decrease throttle, and you should be able to decide if the problem is due to the engine thrust line or the wing incidence.

JimTrainor's test of quickly pulling back the power is aimed at determining the same thing, unless I'm mistaken somewhere.

Do check the ailerons as suggested above. It's common on flat bottom wings with strip ailerons for people to set them as a continuation of the top of the wing, which can lead to problems like you describe. Raising the ailerons a bit will help. At the very least, they should continue the bottom surface of the wing instead of the top.