I've been struggling school because of quarantine and online work, and have been doing better lately with most of my classes. But I've been struggling with one class, the one where I told my teacher that I wouldn't push back their work like last semester. But, due to lack of motivation & recklessness, I pushed it back super far up until just a couple days before the end of the grading period. What do I email the teacher to ask if they can plug in the grades? I know I probably don't deserve for them to put them in for me, but I'm terrified of failing and disappointing people.
Frankly, I've no idea what you mean by "do my grades" or "plug in the grades". But I take it you either want an extension (possibly accepting a late submission) or a sympathetic grade.
Studying online screws you over in that regard. Unless you know your teacher's personality beforehand, they know you and your plea is made to look quite earnest, the possibility of charming your way around the facts is remote, as experienced teachers have been desensitised by every excuse in the book. You should still appeal, but don't use somebody else's words because that's unlikely to work in your favour.
To paraphrase a film: "Everyone fails at who they're supposed to be. The measure of a person is how well they succeed at being who they are."
Your parents want you to do well at school because people who are not properly educated tend to have a harder time in life. However, what slips society's notice is that people who are not internally motivated tend not to have a life of their own at all, not in a meaningful way at least. You mustn't fear failure and disappointment as they shall manifest inevitably. What you should do is find out what you still want to do despite not always succeeding or being the best. Acknowledge that you spend all of your time on it, but that a good education and job will free up more time later. That's your motivation.