With little previous experience it is possible that you chafed the skin of the vaginal opening. It may also be possible that if remnants of the hymen still exist that "he rubbed that the wrong way" so to speak.

Here are some things to consider: Were you wet? Did you spread a little on his penis in order to make entry more slippery?

Just because you may produce plenty of mucus does not automatically mean it will be amply distributed around the entire surface of the opening. Attempting to push a dry penis into a partially dry opening is cause for discomfort.

In time and with continued intercourse the opening will tend to stretch. You can get a jump on this by doing some stretching exercises on your own. It is best if you partially fill a bathtub with warm water in order to soften the skin, although keeping the area warm and wet from the water of a shower head will also work.

Insert a finger and tug in one of four directions holding the tension for several moments before moving to each of the other quadrants in turn. Do this daily for fifteen minutes or so and in several days you should find that you can insert two fingers. When you can, continue as before, although tugging or pulling in opposite directions using two fingers of the same hand or one from each.

An alternative plan is to insert dildos like a candle stick, carrot stick, or English cuccumber. The regular and English types of cuccumbers come in different diameters so you can start small and slowly increase the size.

No, you will not continue to bleed. If on the rare chance you do, then see a doctor.

...and please use a condom unless you want kids.

Use spermicidal lube and, as per Browser, a condom.