I had the same problem on my Skymaster Gripen on both the rudder and elevon. I cut the rudder out and installed CA-type hinges along the complete length (approx 6") of the hinge line. I only needed to install a couple of inches width of CA hinges on the elevon. As Dom says, make sure that the control surface is straight. Also, I'd suggest putting a bead of oil on both sides of the remaining live hinge line to prevent any CA from getting into the hinge line and hardening which will cause the it to quickly break.

Regards,

Jim