Is there any way for a High-Schooler to make friends their senior year?

No one really knows how to make friends because no one ever sets out to do it. Friendships just happen. Don't work too hard at it. And don't worry about how it will happen. You'll see that someone likes a band or TV show you like. Start up a conversation about it. Ask what their favorite song is. Or maybe you will find someone else sitting alone. Ask if you can sit with them and then you can start to get to know them. You will have to go outside your comfort zone a little bit, but you can do it. It will get easier every time. And it will be worth it.