I'd say first: work out what you're actually scared of.
Like you've felt this nebulous scared feeling but you've probably never sought to interrogate it, because it's way easier to realise you're just working yourself up over nothing when you actually think about it.
Like, some common examples:
"I'm scared the comic will be bad!"
Ok but so what if it is? Everyone here who's making good comics has at some point in their life made bad comics, bad drawings, bad chapters of books, etc... It's part of the process and everyone who's made bad comics has survived it, you will too.
What if people don't like what I make?
No one who's any good will morally judge you for having kinda bad art or a kind of cliché storyline, and no one who does is worth listening to. Technical critique is useful, but doesn't say anything about who you are, and actually LIKING something is completely subjective. I LIKE reading some books that are just objectively awfully written because I get joy out of it, a lot of people DON'T LIKE some very masterfully crafted films or books. It's all down to taste and as long as ONE person (you) enjoy the comic process, that's all you need.
It's such a long process to make a comic, what if I don't want to do it until the end?
It is a long process, but if you never start, never finishing is a foregone conclusion. Say making your comic idea will take a full year. The time is going to pass no matter what you do, so when we get to 2026 do you still want to be where you are now with no comic pages and the fear and frustration of having these characters cooped up in your head, or do you want to be the guy with a full or partial comic? Because some comic is always better than no comic.
What if I get a better idea later after having done something that means I can't go back and change it?
Frustrating? Yes. But the fun is working out how to work the new idea in well with what you've currently got. Having a couple of drafts and rewrites of your story before going into the drawing phase will help avoid this happening too much, but even then because comics take so much time you can plan ahead and tweak things so they fit your new idea.
If there's anything else scaring you: ultimately, comics don't matter. People read them for fun, people make them for fun (or if they're lucky: for money). You don't owe anyone anything but yourself so if any of your fears are to do with failure: there are NO CONSEQUENCES for failure right now. No pay, no boss, no deadlines, no audience even. Whatever you do as long as you're making the thing you're gaining experience and knowledge and drawing stamina and that's always a win. If you don't want to publish it online because you don't think you can handle feedback: just don't publish it. Still make it though, it'll do you good.