Should I risk it?? (Please read description)

My science teacher has entered 9 grades in the grade book so far. It's half way through the marking period so interims come out tomorrow. I failed a large assignment because I didn't turn it in, but just yesterday, I turned in the assignment and he told me he'd give me full credit. But he hasn't entered in the grades so my grade in his class is a 66% still. I'm debating showing my mom my grades and risk getting grounded, in trouble, and worst of all having her be disappointed in me. Or not showing her the grade and have everything be alright, but that's lying to her and if I get caught she'd be even more disappointed in me. A part of me knows I should do the first thing but I'm tempted to keep her trust by lying (which is SO wrong I know) Just lately I've been so stressed I don't know what to do...