Find mistakes of this conversation's grammar and the right use of modals Gabrielle : Hello Sisca, what do you think about tomorrow’s party? What should I wear?

Find mistakes of this conversation's grammar and the right use of modals
Gabrielle : Hello Sisca, what do you think about tomorrow’s party? What should I wear? Should I wear long sleeve shirt?
Fransisca : No, you shouldn’t wear that.
Gabrielle : Well, how about a casual t-shirt and jeans?
Fransisca : What? You must not wear that! It’s a formal party after all.
Gabrielle : So, I must wear a dress to go to the party?
Fransisca : Yeah, so you could look more elegant
Gabrielle : But, I already bought a long sleeved shirt.
Fransisca : Really? You shouldn’t have done that.
Gabrielle : Yeah, I should have think twice before buying something.
Fransisca : It’s okay, you must have forgotten. People make mistakes, you know.
Gabrielle : Anyway, Do you want to help me find a dress later?
Fransisca : Of course, But I think we’d better buy it right now.