Alternative ways to say ‘thank you very much’

I play with some other people on a sushi restraunt game where we practice our Japanese by serving and ordering in Japanese for fun. I’ve been constantly getting moderated for ‘arigatogozaimashita’ I presume for the ‘shi-ta’ sounding like shit. My only other though is to bump it down to Arigatogozaimasu but that feels a little informal for a ‘waiter’. Someone suggested みたくたありがと but it didn’t sound right either.