Take a deep breath, let it out slowly...and remember --
NOBODY DIED HERE!
So, no matter what happens -- how bad can it be?
Everyone makes a mistake now and then; you've never been in trouble, and no patients were endangered...
Take another deep breath...
If the "worst" happens, what will they do?
Kick you out of nursing school? (I think that's farfetched, myself, since you've never been in trouble before -- and usually it takes a LOT to kick you out -- and it usually has to do with something that is illegal, immoral, or endangering)
Make you abase yourself before everyone you know while screaming, "I am not worthy! I am not worthy!" I personally don't think they'll go this route either
I think you're probably going to be subjected to "We don't want this to happen again, what are you going to do to solve this problem?"
Let us know what happens, OK?
PS We've all done stupid stuff under stress, including your instructors...