I had periods on 17 and last date was 21...i had sex on 27...if there are any chances of getting pregnant?

Yes: If you have 28 day cycles then that is probably a little early, however if you have shorter cycles then it is more probable.

Too close to call: If you have a regular 28 day cycle, your date of ovulation would be on the 30th and viability of sperm in female is up to 3 days. So there is a possibility of getting pregnant. If you have irregular periods then calculation is changed...