There are never any guarantees about complications. The only certain thing is that if you do your best to keep within reasonable range most of the time, you'll massively improve your chances.
Don't sweat it too much if you're out of range now and then - happens to all of us.
It's the bigger, long term picture which counts. You're not going to be suddenly blind or losing limbs if you're out of range every now or then provided you put some effort into minimising that.
Complications don't happen overnight. They're most likely to occur when people go into denial, pretend they're not T (I'm aware from your earlier posts you're still a bit uncertain, pending tests, about which type you are!), and run around in the twenties as if they weren't T at all.
If I was you, I'd push complications to the back of my mind, because you're still really early doors with this, and focus on the day to day things which you'll need to learn to cope with the reality of it.
Do that, and complications will become something which your docs will pick up on and treat if they happen, and there's some pretty **** cunning things they can do nowadays.
One of the things which motivated me a lot to pay attention shortly after dx was reading an article about a girl who got some serious eye problems five years after dx, because she didn't take it seriously, running in the twenties a lot. I decided I would pay attention because I didn't want to go blind. Thirty years in, I'll say that again, in case you didn't notice the first time, thirty years in, my eyes are fine. Not through any restricted fad diets, just through making careful decisions about how much insulin to take.
Like I say, there are no guarantees in any of this, but the chances of any bad complications happening to you are pretty minimal provided you pay a bit of attention to it.
PS: the girl in the article I mentioned listened to her doctor, paid more attention, and turned round the eye problems. Result!