how do I change how many weeks I am?

Melissa • ❤️🤰🏽💄💋
So I went to planned parenthood on Wednesday and they said I was 4 weeks and 1 day but the app says I'm barely 4 weeks and 1 day? Who should I believe lol. I have an appointment tomorrow but idk if they would even do a ultrasound yet!??
Help...