Ftm advice on babies bottom

Victoria

I just changed my 2 week old baby girl and her butt seemed red, she is bottle fed and i know you are supposed to keep a babies bottom dry but idk how to since the hospital told me not to use baby powder until she's a month old ... could she have a rash ? i have diaper cream should i use it ? was the hospital wrong and i can use baby powder ? should i let her bottom get some air ?