I'm cd27 today and just tested with a digi hpt that came up not pregnant

on cd23 I had a bright red streak in a clear long cm followed by a pale pink smear on the loo paper so hoping it's implantation, is 4 days after a possiable implantation still too early to test?
I would have thought in 4 days it be at least at 50?

Obviously it's not over till af shows up, but I'm curious as to if this was implantation.