If the line is thin, it's an evap, if its the same thickness as the control, it may be positive.
Test again with a pink dye test in 2 days. Clearblue are terrible for early testing. So many evaps after such short times and indents (indents can show immediately). I wouldn't trust a clearblue line unless it was a thick, obvious blue line.
Seen so many people get what they though were v faint positive clearblue but negative on other tests and negative blood tests.
Absolutely baffles me that frer have been discontinued in UK stores but clearblue are still around, they're so bad.
Faint lines at 12dpo are totally normal though and a lot wont get a line at all at 12dpo. Implantation is at 6-12 dpo and you have a base beta hcg between 1 and 5, so it's entirely plausible for it to take up to 7 days after implantation (most commonly 8, 9 or 10dpo) to show on a 10miu test.
My v faint positive was on 13dpo. Shadow of a line that needed the saturation maxing out on a pic to show obvious colour.
Have you retested yet @tedmarie