Oh wait what? It shouldn't sit in there. You need a T-Adapter for SCTs that threads onto your scope. http://www.amazon.com/Celestron-T-adapter-Schmidt-Cassegrains-Threads-Cell/dp/B00009X3V8
I'm not 100% sure this is your problem because I've never used my SCT without the proper t-adapter.
I have this for my C9.25 http://www.amazon.com/gp/product/B00009X3V8/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1
It threads onto the back of your scope, and then the camera end t-ring screws on the end of this thing. (Actually, mount it all to your camera, THEN to the scope)
Double check that your scope is supported. I would think it would be.
Is it an SCT? If so, you need this http://www.amazon.com/Celestron-T-adapter-Schmidt-Cassegrains-Threads-Cell/dp/B00009X3V8 because you screw it on, not insert it.