How can I stop feeling like a failure for not graduating on time?

In tenth grade I went through a lot of problems and stopped going to school for about half a year then eventually go put into alternative school. Whenever I went to school I worked really hard and did great but there were a lot of periods where I was depressed and didn’t have the motivation to even get out of bed.
Now as the new school year is starting, I should already be graduated but I still have a couple of courses to go and I feel like an idiot. I feel like I’ve let everyone around me down and my sister is always making fun of me saying she’s going to graduate before me, I want to do something with my life and honestly, I kind of want to re-do some courses and get better grades but im so ashamed of myself for not being done that I feel like I just need to get it over with. I find myself not even wanting to go because im so depressed about it, what can I do?