Ahh, I see now. Yes, the elevon (or v-tail) setup can be annoying but it looks like you are almost there.
Step 1 was to use the Elevon Planes section in the Wiki.
Step 2 was to use the RC Inputs or RCMAP, which you have done.
Step 3 is to get the reversals right as kikislater suggests. Keep following the Elevon Planes section until you get to Servo Reversal. This section explains what to adjust. I needed to read it when setting up my mini Talon using v3.8.2 for the first time. The new procedure will soon become our old friend. Hopefully, Mission Planner will catch up to the changes soon.