When a dancer rehearses his part of an intricate choreographed dance, he has to trust that he’s fitting in with the rest of it. That’s sort of what you’re doing. You’re doing what you learned to do, with craft; you’re telling the story your mind has created. Trust yourself and work forward.
Trust that it will be good when it’s done, or at least that you can rewrite it so it’s good. Trust yourself — which can be really difficult.
And you think, “What if it’s too ungrounded and makes no sense? What if it’s too slow? What if it’s boring?”
It might very well be. Or it might not. You won’t know till it’s done. Once you’re done, your beta readers should be able to give you a clearer idea of whether you messed up or not.
Sometimes I still get: “Your opening is slow. This is where it got better.” And then I go back and study whether it’s true or a reflection of that reader’s particular bias. (Yes, that happens too. Some people don’t like novels that start with jail escapes, or novels that start with the character asleep, or whatever. Readers are people too. This is why you need more than one — so you can check them against one another.)
The point is that if it turns out to be too slow, once it’s done, you can always go back and rewrite it. But not until it’s done.
For now, you just can’t tell. Keep your head down. Keep working. Keep your figures in the dance and trust that it all works out.
Don’t let your insecurities morph into an excuse to not write. The world is full of people who started a novel. There are far fewer people who have finished a novel, let alone multiple novels. Your goal is to write and keep writing.