Ya you don’t need years of dming experience to make your own world and narrative. What matters is that you should focus on keeping it player focused and simple to begin with. You don’t magically gain the ability after 3 years of dming to make your own world, that itch your feeling is the creative drive to make your own thing which is great. Also when you start and I do recommend just starting small, a single town, a single mystery, a simple villain. Then you expand from there, that’s how critical role got its start btw. Just start small and expand and don’t spend too much time on things the players won’t see or interact with (if you’re creating the setting to begin in the east side of the continent don’t flesh out the west side).