There is nothing to worry about conception just before a period as it is absolutely safe. The spotting could be premenstrual. It does happen sometimes when there is a mild hormonal
imbalance owing to stress
. Please wait for a couple of days for your period to set in. You can see a specialist if you do not attain a proper period for further appraisal of the situation. Do not worry, there is absolutely no chance of conception with intercourse, even if unprotected, just before a period. Hope this helps.