Hi, my cycle is regular 24 days. i had sex on day 3 using withdrawal. was it safe day? around when is my ovulation? what is the chance of pregnancy?

No: There is no such thing as a "safe day" unfortunately. I think my mother told me I was conceived on her 4th day of her menstrual cycle. Withdrawal has about the same effectiveness as condoms in terms of pregnancy prevention, so it helps, but is no where near perfect. The chances of pregnancy with one encounter are low, but not zero. 2 methods of contraception is best to prevent pregnancy.