HELP!!!!! I have a freaking D(68) in Geography!!! Lowest grade ever!! I usually get high b's and a's!!! Omg!?

I've never made this kind of grade before. I flunked the 2 test we had(58) then the 3rd test I made a 36 then the 4th test I made a 58! I have a D in there! I've never had that happen. How to bring up fast before my parents notice, I'll be grounded for sure, and I'll be in BIG trouble. PLEASE!!!! Hurry!!!!