I was due for my period on 20th June however I had sex 3days before I was due on 17th I did a pregnancy test today&it came back negative but I'm still late for my period. Is there any chance I could be pregnant?

Possible, but it is much more likely that your cycle is just off a bit. Give it a bit more time. If still no period after several more days, try another test or you could see your doctor for a test there.