Don't worry, it's not uncommon! I had a panic moment during my discover scuba.
I was mostly excited and a little nervous after the short orientation we received. We were gearing up and I was trying hard to reassure my girlfriend, who was admittedly extremely nervous. I didn't realize it but small stressors were mounting against me and I wasn't doing much to keep my own pace in check. We then had to wadd through a breaking surf to work our way to a calm area for our confined water portion before swimming out. The first moment of putting my head under and sitting on the bottom was kinda terrifying. I didn't shave, so water started flooding my mask. We were in a calm area with no waves, but I could feel the swell and pull of the ocean. Oh yeah, first time in the ocean lol. My fingers started to tingle in that panic attack fashion, and I remembered what the instructor said in the little classroom. Stop, relax, think, act. So I stopped looking around, closed my eyes. OK, they showed me how to clear a mask. Hold the top and blow, holy crap it worked! I opened my eyes and the instructor was signaling, ok? OK, I'm ok. Did the skills, went for a swim, and had the time of my life.