I use my depression as an excuse for not going to school and not working and I hate it.
That's awful. Why do you hate using your depression?
I would much rather sit in the emergency room for 15 hours than go to school, but I feel guilty.
It's fine to miss school sometimes due to depression. It happens and everyone is depressed sometimes.
But I hate that I feel like I am "abusing" depression to get out of work and I hate it that others might think that.
But you know that your depression is real and that you need help. To get help for your depression is more important than school and work. So concentrate on that  you are doing what you can so that you can do better in school and work and don't worry about others.