No offense to you guys but I think that you are misleading him. I agree with cmoretti the heavy bleeding sounds exactly like a period. It is not a miscarriage. some women ovulate pretty late in their cycles but the endometrium is sooo thick at that point that the chances of implantation are extremely low so she will not get pregnant. She had her period right on time so it is VERY UNLIKELY that she could be pregnant.
If it makes you feel any better, wait until her NEXT period, if she is late (for more than 5 days) then take a test.
But I don't think that you have anything to worry about. However, please use protection when you have sex, always.
There is no way that she could have been pregnant, at that time, if you had sex 3 days before her period. Even if she happened to ovulate on that day, it takes over 6 days for the egg to travel to the uterus and implant. So her period was a normal (abnormal for her) period. You need to have more than 10 days between ovulation and period to sustain a pregnancy. 3 days won't do it. That being said, if she did O on or a couple of days after you had sex, It is possible although highly unlikely and very rare that she COULD now be pregnant. If the egg didn't get to the uterus until after she was done with her period then it could implant. Unfortunately she will need to wait about 14 days to test.
You'll have to wait about 14 days from the possible date of conception (June 3rd) to take a hpt. I highly doubt she's pregnant as her period came as expected and because you had sex so late in her cycle. But there's always that small chance so you should definitely test to give yourself some peace of mind. I agree with the above poster about using emergency contraception (Plan B) in a situation like this but that would not apply to this particular situation as you're already past the 72 hr gap indicated for that pill. Please keep in mind that something done "spur of the moment" can easily turn into a lifelong obligation/commitment so you should practice safe sex or abstinence when pregnancy is not a wanted outcome. Good luck.
Heavy bleeding with strong pains is usually a bad sign(usually results in miscarriage) if she is in fact pregnant although I don't think you and your GF have anything to worry about. Light bleeding in early pregnancy is normal in most cases. I would take a pregnancy test to make sure and see a doctor. If you are very worried then you can buy PlanB in any pharmacy. Your girlfriend can get it if she's 18yrs or older and it's over the counter. It does not terminate an excising pregnancy. You can read and ask more details about PlanB to any pharmacist near you .I hope this helps. Best of luck-Kelly