So nervous about potential chemical pregnancy

Got my first BFP on Sunday, also tested yesterday and today. Lines are getting darker but had some brown spotting. Day 25 today, AF due Thursday. New to the ttc community and had I known what I know now I wouldn't have tested early! Worried it might be a chemical pregnancy. Never thought I'd be so nervous about possible mc, but have realized how precarious pregnancy can feel and why pregnancies feel like miracles. Wishing you all your own miracles!