I'm a healthy 20 yr old i had unprotected sex on either day 7/8 of my cycle what are the chances of being pregnant if i have a regular 28 day cycle?

Possible : Anyone having intercourse without birth control or condoms may get pregnant. If intercourse was within 72 hours you consider taking plan b. Ella (ulipristal acetate) is another brand that can be used up to 5 days after unprotected intercourse. Plan b is a high dose of birth control to disrupt the hormonal patterns to delay or prevent ovulation. Abnormal bleeding after is common. Check preg test in 10 days.

Yes, small chance: You can get pregnant anytime during your cycle, albeit less of a chance around the time of menstrual flow. The chance is much higher during time of ovulation--mid cycle for most folks, but it can happen at any time. If you are not planning for pregnancy, always use protection. In this particular case, chance is low, but it can happen--wait a few wks and see. Consult doc for problems. Good luck.