The only way to make friends is to go out and meet people.
The only way to make lone time is to schedule some, and think up ways of making sure it really is time on your own.
School is a relatively structured environment, and a good place to make friends. You don't have to rush into friendship - take your time to work out who is genuine and nice, and who isn't. If the environment seems overwhelming you must remember that you have lone time scheduled for that evening, or at the weekend, so it's not as though you'll have to wait too long for the space you need. It might also be worth considering options for reducing the levels of stress that you feel in busy situations. Whether that be through anti-anxiety meds, hypnosis, yoga, meditation or whatever. Maybe even something as simple as wearing headphones so your music blocks everyone out if you want some space in break times, or breathing exercises. These things won't stop you from worrying / feeling overloaded completely, but they might take the edge off it enough to make it manageable until you can get away.
If you want to try and make friends outside of School then joining groups is probably the best way. Have a look at something like Meet Up. It's said that AS people generally get on with other AS people the best, though I'm not sure that's true, but maybe finding a local support group would be a good start? Or alternatively maybe a group of people who exhibit AS-like symptoms even if they don't know it. For example I've just joined a Meet Up group near me created expressely for self-confessed technology and design geeks.
You don't say what your home life is like but again it's a question of making some safe space for yourself to be alone. If that's not possible indoors then can you go out? Sit in a garden or yard? Go somewhere where interaction is frowned upon, such as a Library or swimming pool? Meditation groups are also good, becuase although you are not alone you do get an enormous amount of space inside your own head, and it's quiet and relaxing.
I don't entirely know what you need but I hope some of these ideas are helpful. It's certainly better to get out there and try than it is to sit at home worrying. And the more things you do, the easier it gets.
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The Sociable Hermit says:
Rock'n'Roll...