Panicking over a phone call

I just called this guy with the intention of telling him point-blank that I have a crush on him, knowing full well there's a giant possibility this won't end well or to my liking. He did not answer. I left a casual-sounding (I hope) voicemail saying simply to call me back when he gets the chance because I had to ask him a quick something. It's been a half hour since I made the call. I'm going to be a hot mess until he calls back, if he does. There's little to no reason why he wouldn't, but my imagination is exploding with the worst case scenarios.

Trying to calm down. I wanna barf. Anyone going through similar things?