What you just got told was info that should have been covered in your OW class and demonstrated to you in at least one of your pool sessions. In fact a proper weight check should have been done in every session. If it was not you have to wonder what else you did not get taught that you should have? The weight check in the pool is the only good way to start. How the suit fits, that it is new, what your body type is, etc all will come into play. How much buoyancy does your other gear have. Many jacket bc's have 4-6 lbs inherent themselves, a BPW none or may be a bit negative with a wing fully empty. Go back and ask your OW instructor what else did he/she leave out of your class that you now want since you paid for it.