I empathise with your feelings my friend.
I've actually had social anxiety all my life (I'm 23), but I didn't really realise I had it until my late teens. I've managed to crawl out of social anxiety a bit in the last few years. Don't get me wrong, I still struggle with the emotional side of it (e.g. feeling drained often).
It's always a constant loop of the worst-case scenario in my head and it's practically torture. I want to reach out, I'm trying to reach out, I'm trying my best, but it still isn't enough! I keep getting caught up in those worst-case scenarios, I keep stopping myself from making friends and connecting with others, I keep telling myself that it's better to be lonely than risk being hurt even though I know it's not true.
Firstly, try to switch off and open yourself up to possible embarrassment. I know how hard that seems, but everything POSITIVE I've ever done in my life happened because I just thought "You know what, I'm just gonna go for it and see what happens". I know the mind tells you that things will go wrong and you'll make a mistake and you'll be so uncomfortable that it'll kill your internally. Trust me! You WILL feel sooooo much better for taking your chances!
Secondly, it's totally normal (especially in today's cynical world) to feel like you want to isolate and be in your own safe space if you like.
Thirdly, try keeping a diary! I'm not talking a classic morning night diary, I'm saying to a notepad with you wherever you go and when you feel slightly wobbly (anxious, lonely, a general feeling of fear in your stomach), open up the notepad, write the date and time, and just write exactly what you are thinking. I started doing this a few years ago when I felt low, and just the act of writing exactly what I was feeling without feeling I had to lie made me feel slightly better.
Sorry if these pieces of advice are not very expert, I'm only offering some methods that worked for me as I have the same issue!
Best of like my friend! Life DOES get better, and it always tend to happen when you least expect it so carry on plugging away and it'll come!