Worried about leaving work early?

im 18 and i do openings for mcdonalds. i have to be there at 4:30 a.m tomorrow to open .. thing is im nervous about telling my boss that i need to leave by 9, because the rest of my family is going to visit my aunt in the hospital and shes sick with cancer, my 5 year old sister is sick, so they need me to stay with her. bringing a sick person around a cancer patient obviously isnt good. i got there at 4:30 a.m today, and i said my aunts dying in the hospital so it would be really nice if i could get out a little early to see her, but they kept me there until 2:30 today. so im nervous theyll tell me no, and that i cant leave early. i dont know what to say or tell them, but i really need to leave by 9a.m.