If you are POSITIVE that is is 4-6 days before you expect your period then it is unlikely you will get pregnant. You would be on days 22-24 of your cycle. Most women ovulate between about days 11 and 16. The egg only is viable for about 48 hours. So, odds are that it was "to late."
There is always a chance but it seems unlikely in this case. Your fertility would be decreasing rapidly.
If you have a "normal" period then it is VERY unlikely you are pregnant.
Hope it helps.