Chances are, it's not an accurate result. Pregnancy tests measure pregnancy hormones in your urine, and the hormones aren't produced until an embryo has implanted into the uterus. Generally, this can take from 5 to 12 days beyond ovulation, with the average being 7 days. It can take several days beyond implantation for enough hormones to be present in your urine to have an accurate result on a pregnancy test. It seems that 8 days after possible conception is too soon for a positive result. Wat a few days, preferrably another week, and test again with first morning urine, as this is the most concentrated with hormones.