The inside of the aileron moved more than the outside, I think because the control horn is on the inside. Being a plastic coroplast aileron could it be flexing?

Yes it could, and that's not good. Most of your roll control is on the outside half of the wing. You might want to replace them with hard balsa. Before you do that, however, check your hinges and make sure they all move freely.

The second thing is that it seems like the push rod is stiff.

That's a straight-run pushrod that's completely outside the wing. It should move freely. Angle the horns so they match the angle of the pushrod.

Dr.1