Till was under by exactly 40 dollars. Unsure of how this happened am i getting fired?

I struggle alot with number, i have adhd and i was the only one on shift as my coworker no called no show. I usually question myself alot but i feel like i did give back the right change, we had a lot of customers ordering weird orders and changing last minute and my manager was on my till a few times to speak to spanish speakers. It was reported bc duh but im so anxious.