Wiktionary
scared as hell
a. (context simile English) Very scared.
Usage examples of "scared as hell".
I found myself whispering back, red-faced at the realization we were two naked slaves trying to talk to each other, scared as hell the handlers would hear.
You never know whether they really want you to stop, or whether they're just scared as hell, or whether they're just telling you to stop so that if you do go through with it, the blame'll be on you, not them.
He was, if he thought about it, scared as hell, figuring Marie wasn’.