5 days ago I had a BA, 500cc HP, but they don't seem very big. Are they likely to get any smaller? (Photo)

It's too soon to be evaluating your results.  Give it a few months to let your swelling go down and implants to settle and re-evaluate at that time because they will change a lot over that time.  Try to be patient. ac

I'm sorry to hear about the concerns you have after breast augmentation surgery.  It may be helpful for you to know that it is not unusual for patients to feel that they are “too small” or “too big”,   early on after breast augmentation surgery.  Most patients who feel this way early on,  ultimately are pleased with the results of surgery in the longer term. Many patients who feel that they are too small immediately after surgery find, as the breast implants “drop and fluff”,  that the breasts actually appear larger to them.
 I routinely ask my patients  to wait at least 3-6 months before evaluating the end results of the breast augmentation surgery.  This waiting time allows patients to physically and psychologically adapt to their new body image. Continue to follow up with your plastic surgeon; time and patience will be your best friends. By the way, 500 cc breast implants are relatively large breast implants, given your frame.  Best wishes; hopefully, you will be very pleased with the longer-term outcome of the procedure performed.