I think feeling this way makes you a perfectly normal 18 year old.
I just want you to know, you're not alone. I "missed out" on all my normal teenage years too -- I didn't go to HS, wasn't even really homeschooled -- I was just very ill during that time. I lost a lot of the friends I'd made earlier in life and to be honest, never really reconnected with most of them. But being set apart at that age taught me something really liberating:
For most of our early life, we're set on a track that sort of runs on rails. You know - one grade after the other, everything is sort of laid out for you. Not having to worry about what comes next (because it's already been decided) feels very secure. When you've "jumped the tracks" and gone off-course, and you see your peers marching along, it feels very scary. You feel like you're missing out on what you're supposed to be doing, and when you know you can't get back on those tracks, it's terrifying.
The thing is, adulthood is exactly like that. There are no tracks. It's a choose your own adventure. That doesn't mean you're happy with how life has gone in the past few years, or even that you really had full agency to make your choices. But you've had experience living outside those set boundaries, and that's very valuable life experience. You have something those other 18 year olds don't. You already know you have to chart your own path, and that sometimes it's very painful. You're ahead of the curve.
For me, I realized I was really OK with having "missed out" on all the regular stuff that teenagers do, because a lot of that typical stuff just wasn't very interesting to me. Realizing that helped me move on from the sting of missing out just because I was "supposed" to do this or do that as a teenager. That may not be the case for you, though, and that's OK too. Can you list specifically what it is you regret not getting to do? Because life is very long. Your late teens and early 20s will have plenty of opportunity for you to make your own choices and choose your own experiences.
There is no way to "live right." Like I said - you realize that adulthood is all about the absence of tracks and "should haves." Sure, our culture has certain ideas about milestones - driver's licenses, jobs, school, marriage, kids, etc. But every single one of those is optional, and no one is a failure for choosing something different in their life. I promise you, there are a whole lot of adults walking around without licenses and they're not weirdo freaks.
I didn't get mine until I was 19, since I didn't go to HS. But I know 20 and 30-something year olds - employed, perfectly well-adjusted ones! - that still never learned. It's OK.
Sorry this is so long. I just really relate. I remember feeling how you did. It's scary. But the main thing is -- it's OK. You're OK. Your life is perfectly OK. You haven't failed. The past can't be changed, and that's OK. If we aren't happy with how the past went, then we have to use that as motivation to grow and to change what we can.
Hugs. You sound like an incredible strong young woman to me. When things seem too hard or too terrifying to move forward, just remember how much hard stuff you've already conquered.
Edit to add -- congrats on finishing high school, that's a big accomplishment.