I’m only a month into it and Ive found that if my resistance is too low then I can feel unstable out of the saddle. If that’s the case I just sit back down. Beginner rides don’t leave the saddle to begin with. They introduce leaving the saddle in advanced beginner classes. And again, if the resistance is too light to stand up then sit back down. Or if you want you can just turn up the resistance to a level where it feels more natural. Regardless, give it time. Your body is going to need some time to get used to all of this. I’m 51 and I know my body certainly did. Good luck to you.