Jessica, no surgeon can guarantee you a certain cup size. It also depends on your back measurements. Like I used to be 36B, then after I lost some weight I became 34C.. But I assume 550 overs will turn up Very big. I don think you’ll be disappointed from other girls I’ve seen with a similar implant size.
To be honest sometimes I wish I went for 500 overs he’s offered first, but I insisted I wanted unders and he had to drop down to 400:( they look bigger from the initial 250 anatomical ones I used to have, but so far a bit disappointed in my volume 🙁 I tried M&S sports bra..34D. So.. Yeah well.. I suppose for my 5.4ft hight it will look ok.