Please help! BFP or old HCG?

Hi guys. I miscarried at 12 weeks in October. I ended up having a d&c in Mid December. I had been bleeding the entire time. Right before the d&c my HCG levels were at 18. I stopped bleeding a few days after d&c. I tracked my ovulation and ovulated/got my lh surge in 1/4. I took a pregnancy test yesterday, 4 weeks or more after d&c and had 2 BFP. Could this still be leftover HCG even though my levels were still so low prior to the d&c? Thank you!

Also- I never thought to test HCG after d&c with hpt so I have nothing to compare it to.