finally got my BFP, but.....

Laura
So I've not been on here for a while. Me and my partner had been trying for a baby for years. We broke up in December (still sleeping together) got back together at beginning on Feb and discovered I'm pregnant! 
Thing is im getting treated by early pregnancy unit because I'm bleeding. I'm on day 4 now of period like red blood bleeding. (Sorry tmi) 
I had my bloods done yesterday which showed 50/muI (HCG level) They are concerned that it is really low and that I could be having a miscarriage. But I've looked online and 50-80 is normal for 4 weeks of pregnancy. 
They checked my cervix and its closed. 
Anyone got any success stories to tell me or advice or just anything because I'm so worried right now. I have an ultra sound tomrrow to just make sure baby isn't in my tubes xx