Most Day 2s are around 4 cells, so an eight cell is great! Dark blood (brown) usually isn't irritation from the pessary, that would be pink (from fresh blood), so it's possible it's implantation.

And I reckon I wouldn't test any earlier than 11dpo, but even then it's 50/50 whether you'd get an accurate result. I got a definite -ve at 11dpo with Charlie.

ETA Clare, you're doing great! You'll get the hang of it in no time!