The aileron should be in the same plane as a line drawn from the tip of the wing to the rear. So, midway.

You will have a gap between the fuse and the ailerons, but did you say that one aileron is longer than the other?

If you are new to RC planes, you probably do not want to fly that plane. It is a 3D plane and is very difficult for beginners to control. You need to get a trainer as your first plane so you can develop your skills without quitting from frustration or destroying your plane.