[kidakaka]

Firstly, have you seen the catapult? Do you access to a similar one to do your test runs on each of your prototypes? If not, then modelling the glider so as to get the best out of your launch would be priority.

What degree would the catapult launch your model? Is it variable? Remember your projectile motion concepts ... for the glider to work, the model must be very robust ... think of a better way to put the model together - cellophane tapes, glue, et al should be avoided. For the model to really glide, your lift under the wings has to be just right, plus having the ailerons (those things at the back) would be a good idea to stabilize the body.