HPT after 12 hours?!

hi ladies.. I had a miscarriage at 8 wks in november. I've had one period since and am currently cycle day 38. I'm usually around 28-30 days so naturally got my hopes up for a rainbow! took this test yesterday afternoon and it showed negative after 2 minutes. I threw it in my bag and carried on my day until this morning when I remembered it. got it out to throw in the bin and it showed a faint but visible line. clearly I'm well outside the recommended reading time but I can't deny it got my hopes up! I took another different brand this afternoon which shows negative also. bit confused!!!