Final Step - How do I get my screen to stay in?

I successfully navigated the replacement of my battery - and having cracked the screen while doing so, replacement of the screen and the digitizer. A miracle - it works even though I have a couple of screws left over and seem to have lost the light sensor. However, I can't get the screen to pop completely back in, never mind get it to stick down. Any tricks to doing this? I'm afraid that having come this far I'll crack the screen again. I may resort to duct tape.