Question is this assault or rape? Help

So my fiancé and I we’re having sex and he ask if he could put the tip in my butt. I’ve told him I wanted to wait till we we’re married to have anal sex, something I’ve never done before. So he says just the tip as a preview, I agree to that but then he puts half of his dick in my ass. I didn’t know he had put half of his dick in me till the next day when he told me. I just start crying feeling violated, Is that considered assault or rape??? Am I just being to sensitive? Please help.