I don’t want to be one of those “speak to the manger!” people,

You’re not one of those people if you’re making a reasonable request for something you’ve paid for! You need to tell her so you can get your money back and find another photographer on such short notice. Most are already booked for Christmas. Btw mini sessions are different than full sessions, it’s probably why she didn’t try to fit you in to her mini schedule

Ooooo this is such a good idea!

You should communicate this to the tattoo shop just in case (if you didn’t already). Just say something like “by the way, I did just want to let you know, I’m just starting out. If you’re still ok with me coming by, but I will understand if you’d prefer I not.” Or something like that.

“so who are you and why are you here?” and im just going to die of embarrassment

Why would you die of embarrassment? You’re the photographer there to take a few pictures. You’re gonna have to get comfortable being around strangers and making them feel like they’re your best friend if you want to do portraits