Unprotected sex but didn't ejaculate. Chances of pregnancy?

So my girlfriend and I we were in a hot tub we had sex but my question is we had some foreplay before we went into the hot tub so I pre-ejaculated then I went to the bathroom before we got into the hot tub. after got into the hot tub after about 10 minutes we had intercourse but it was maybe 10 to 15 seconds of insertion but it wasn't full insertion but I did not ejaculate before we stopped cause we didn't have protection. Her period is coming up and I'm wondering the chances of her being pregnant under those circumstances we are just paranoid!!