I need help

So, my fiancé and I got engaged last month. I didn't tell my family right away because him and I had only been dating for a little bit. My mom eventually found out, but my grandmother and uncle still don't know. Then last sunday I found out that I am pregnant. Again my mom found out, but the rest of my family doesnt know yet. My grandmother is a very strict Christian and said that I won't be to be a sunday school teacher at my church if people find out that I'm pregnant, but not married. I have to tell them today because I'm afraid of them finding out everything from someone else. I don'tknow what to say and I am absolutely terrified of losing my family. What should I do?