I would call and see your doctor. Cause usually it takes 4 weeks to get a positive pregnancy test, and if you had a miscarriage 3.5 weeks ago, then it can still be the hormones from the last pregnancy. Idk I hope I'm wrong though. I hope this is for real :)
I got pregnant about a month after a miscarriage, and I'm now 36 weeks pregnant.
I think you should get it done at a doctors cause since you recently had a miscarriage you can still have those hormones which makes that line appear. I know because that happen to me.
You should try posting this question on the 35+ because they are older and most of them would know