You shouldn't just arbitrarily go to full opposite aileron. Many planes with wide and powerful ailerons will roll out of the flat spin at full opposite. Get into the normal spin and go to full power. Then ease the aileron over watching the plane. You should see the wings leveling out and the nose raise. Find the amount you can take without kicking out of the spin and stop there.

Many planes won't get really flat, but they will enter a "flat spin mode" with the wings more level and the nose higher than in a regular spin.