Agree with this, also, if you need to reverse a servo on a Y, they make reversing Y's that will allow you to accomplish this, they also have some with an adjustment pot for trimmining center. They run about $20.00 or more.
ORIGINAL: Maudib
That's not normally how bipe ailerons are mixed...
You plug the left wing servos into a "Y"
You plug the right wing servos into a "Y"
THEN mix the two using the Aileron and AUX channels.
On Futaba I put the right aileron in the aileron channel (1) and the left aileron in the Flap channel (6)... then enable flaperons.
If you have to reverse a servo (usually a pair on one side) simply reverse the channel they are plugged into...