How do i tell my parents"?

Today i took my biology final. Its a scantron and i checked with my teacher after and asked her how well i did. I got a 58. with a C for the year including the final. I have never done really well in bio, C's with some D's here or there. I ped my midterm with a 62, but my parents expect me to get C's or so. I did study, but i never do well with multiple choice (the whole thing was). Point is, I know my parents will get my report card eventually, so i want to know if i should let them find out then and pretend to not know what i got until then, or if i should just tell them. Im scared of their dissapointment.