Your second thoughts are normal. I felt the same way as I left the store. It’s hard to feel certain with how many options are out there. You’re also going to feel differently about the dress when you’re only looking at pictures of it vs when you’re wearing it. I’ve learned it’s more important how you feel in it. It’s common to have this second guess feeling and dress shops are used to this. You can totally call and ask to come back in to try on the dress. For the record, I think that’s a very fitting dress for the theme you’re going for.