My cycle is usually 26-28 day cycle. my last period was 4th july, if 28 day cycle means my ovulation could happen on july 18 (before 14 days of next period) if i had intercourse on 20th july( after ovulation) . is there chance of getting pregnent?

Yes. Pregnancy is known to have occurred from sex on any and all days of the cycle. It is too late now to take Plan B, if you do not wish to get pregnant. If you miss your period by 4-5 days, do a home pregnancy test. If the result is negative repeat it 4-5 later unless you get a period by then. For info: http://www.nichd.nih.gov/health/topics/menstruation/conditioninfo/Pages/causes.aspx