If you have a computer radio capable of using a different channel for each servo, then there is no need to "mirror" the servos.
I do not have that particular plane but I asume that it is a fault in the design. The common is that servos go "mirrored" installed.
If you do not have a computer radio then you can use an X-acto blade and carefully cut into the aileron covering and balsa sheeting, ad a block of wood where it needs to be, replace the balsa sheeting (if apply) and the covering.

I hope this can be of help.