I am unsure of how you messed up the first one, you may still be OK.

What you do is........
You start with the sheeted core and mark out the ROUGH outline of the aileron. Let's say the AILERON is supposed to be 3" wide. Mark and cut at the 3" wide line. What you will end up with is an OVERSIZED ailreon and WING TRAILING EDGE. They are oversized BECAUSE you still need to trim them off so you can add a BALSA LEADING EDGE to the AILERON and a BALSA TRAILING EDGE to the wing.

Now you have the 2 pieces. Mark and CARFEFULLY cut them so you can add say a 3/8" balsa edge. Take your time and cut close to the line then sand flush to the line. Then sand a little clearance between the AILERON and the NEW WING END (where the two come together on the inboard part of the wing. Install a ROOT CAP to the Aileron and an END CAP to the NEW WING END. Use TITEBOND or PRO BOND wood glue to install the leading and trailing edges. Trim sand the ends and BEVEL the edges for throw.

this should get you close. hope it helped