FWIW, and for good or bad, the age of consent in Maryland is 16 for both male and female. If you are both of at least that age and one of you is not 18 or over, and have consented, you are on LEGAL ground, but not necessarily moral ground. Fathers protect their daughters, probably because we were young once and understand what young men are preoccupied with. When something goes wrong, it is usually the girl who pays the heavier price. We want to prevent that one moment of unbridled passion from becoming a life changing event.
Be honest, contrite and sincere. If you and your GF want to continue seeing each other, hopefully the father will accept that. If not, then, of course, Alpster's synopsis becomes truth. If the father does permit you to continue seeing his daughter, I wouldn't take that as a license to continue your behavior. Was this consensual between the two of you? If it wasn't, I certainly wouldn't try to present it as if it were. Man up and take full responsibility for your actions.