how long after miscarried will I get positive test for

I was told to test in 3 weeks and if negative which they said should be I was 5-6 weeks at the time I miscarried then I'd be ok but if positive I would need to go back for dnc which really scares me anyway I took this last night still very positive it is lighter than what it was before I miscarried  'm so scared to go for dnc I've blead loads lost loads of clots to my bleeding has stopped completely should I Leave ot just another weeek and then ring hospital back just to give it chance to become negative