You can make thousands, but the Compound gets crowded and you can only keep 50 at a time. So sometimes you will need to let some hybrids go in order to make room for new ones. To release a hybrid, go to the compound and press the "Release Hybrid" button. A message will come up asking you to confirm that you are ready to let that hybrid go; once you choose "Yes", the hybrid will be gone for good.

You can also release a hybrid if you try to save one when you've reachd the maximum capacity of your Dino Compound. A message will come up in the Hybrid Creator letting you know your Dino Compound is full and you'll have to relaease a hybrid to save a new one - from here you can either release a hybrid and save the new one, or choose not to save the new hybrid you just created.