This is literally my very first job (not counting babysitting etc). You’ll be fine.

I never worked in any food related place before i got hired; when i got interviewed she loved that i was experienced with having people sign up for credit cards at my old store, as starbucks has the rewards program we want to get people to join. It’s also attractive to have open availability for the most part when you’re filling out your application. So maybe when updating/making a resume for the application mention any experience you have related to opening cards/rewards programs, cashier experience is already a big bonus, and so is open availability 🙂