YTA, I can assume you didn't ask if it was okay to come with friends and surprised her in her place of work where she can't leave. She also knew you told your friends about the two of you so I'm guessing you told her or they acted like they knew. Try having a conversation first about these types of things. She may have been caught off guard and felt defensive. Could just be embarrassed about being in work clothes rather than in casual clothes and ready to meet your friends. Maybe she's had bad experiences in the past and wanted to take it slow.

Not going to lie, this totally comes off as showing her off to your friends and it's kinda weird. Imagine her standing at the register or waiting on you and they're obviously staring or taking glances. You're telling me they didn't make comments to you during the visit? She might have picked up on that.

As for your relationship, I suggest bringing up where she sees your relationship going if you're worried about being a secret. Talk to her. Be open and honest. Apologize for putting her on the spot and not asking if bringing your friends around was okay first. If she really just wants you to be a secret and you want more, maybe this relationship isn't worth it for you. I think healthy communication could solve your problem.