Other than having an electrically reversed servo you probably have the servos installed as described in the above post. Look at the bottom of the wing and if the servo arms are both facing the left or right wing tip you will need to flip one in the pocket so its arm faces opposite the other.
If you can't flip one then as mentioned, connect one to RX channel 1 and the other to channel 5,6,7,etc..(any open channel) and program an aileron mix.