Just curious

Hey guys. First pregnancy here! Yay!! I’m so excited. So I just found out like 4 days ago. Went to doctor next day and got it confirmed. He said I would be 5 weeks and 5 days today. But my friends tell me that once I go to my first ultrasound, I could be pregnant less time than that as they go off of my last period. So I thought about going to get one of the clear blue tests that have the week indicator... has anyone had any experience with that?? Was it true? Or was it off completely? I’d like to know before I go buy it and waste my money on it when the time frame is wrong lol.