This sounds like a left aileron stick command is deflecting your elevons equally, but a right aileron stick command is giving unequal elevon throws. You need to make adjustments to make them exactly equal to give you equally axial rolls in both directions.

But before you try to electronically adjust the throws to get equal travel, first make sure the left servo and elevon linkage setup is exactly a mirror image of the right servo and elevon linkage setup. The more attention you pay to details about mirror imaging the left and right elevon setups, the better your plane will fly. Then you can use the electronic throw adjustments to fine tune the elevon travel.

All flying wings are much more sensitive to differential throws and CG settings than "normal" planes. But once setup correctly, flying wings fly just as good as normal planes.

Here's my DaWing, which evolved from a King Kombat.
http://mypage.yhti.net/~dmcdnld/dawing.htm