Each cycle you only have a 20% chance of conception (even with absolutely perfect timing). Implantation can take anywhere from 6-12 days past ovulation and then another couple of days for hcg levels to rise (which would give a positive test). Just because it's "Possible" to get a BFP 6 days before your missed period, that doesn't mean it happens for many women. I didn't get my bfp until 14 dpo and many women don't get it until 12 dpo or later. Wait until AF is due and try testing again. Good luck!
This link explains it pretty well
5 years ago