When is every thing officially attached to the uterus?

Isabella
Got my bfp Saturday (6 days before AF) it is getting darker each day, my question is, is the egg and everything already attached to the uterus or has implantation yet to occur? (I know some people say you won't get hcg/positives before implantation but then I've heard doctors tell others that some light spotting after the bfp is implantation bleeding lol