College professor question

Hey guys. So I’m currently freaking out times ten because my chemical engineering coding professor asked me to be in his research lab. Which at first I was super Uber mega freaking out but now I’m second guessing myself. I got 77 on the last two tests and he started changing my homework grades so that they’re LOWER. I got extra credit on a few assignments and I figured I should have at least a B but now I’m at a 77 in the class. So I’m really just kind of like “why did this professor dude pick me to code data for him???” I do go to his office hours and coincidentally we have a lot in common but I’m just so embarrassed that he asked me to join but I don’t have like perfect grades. Or that he might have asked me by mistake and he’ll take back his offer. I have the final for his class today so I’ll see him and ask about how he calculated final grades when he started lowering my grades but I’m just so aghs. I’m already stressed for my exam but now I feel way pressured to do way way better. What do I do?