sometimes when women have endometriosis or even a cyst this can happen. you should rule out any medical reasons by seeing a doctor
Sweetie, be happy you're small. You may have some bleeding in the beginning, as you described, the rest of your days with a new partner, until your body gets accustomed to him - and it may go on a few times if he is well-endowed. This has nothing in the world to do with your cervix. That is the gateway to your uterus, opens (dilates) when you deliver a baby, and has nothing to do with the size of your vagina. Don't worry about this at all, unless you bleed really heavily - enough to soak a washcloth. If that happens, then go to a doctor. BUT what you described is absolutely normal.