@Saribon how you doing? Are you ok? So sorry you're having all this worry. I haven't got an answer as I haven't had a chemical but I know with the MC it took ages to become negative.
I wouldn't worry about the super dilute test you did at EPU contrasting with the faint positive. It's just the HCG leaving your system. They might have discounted ectopic as it's decreased rather than increasing slowly - which is a key indicator of ectopic. Having said that, they should have done a blood test to confirm this.
When I was miscarrying at 5+3 they classified me as pregnancy in unknown location, so potentially ectopic. Whilst I was heavy bleeding they kept me in but once it subsided they sent me home, even though they still hadn't identified where the pregnancy was. It still could have been ectopic but they just "safety netted" me I.e told me the warning signs and what I had to do if my symptoms changed.
It could be that you're still pregnant because as you say, you didn't have a big bleed. Or it could be that you're still miscarrying and the main bleed is still to come.
I know it's nerve wracking but look out for the warning signs (heavy bleeding, heavy cramping, shoulder tip pain, raised temp etc) and go to A and E if you begin to feel unwell.
Please let me know how you get on xx