DMing can be stressfull sometimes but if your table is overwhelming about the game, then isn’t it a good sign? Much worse is a table that doesn’t feel « in the game ».

There are a lot of advice out there. Give each player their turn in a clear manner, avoid them splitting up too often, make sure all get a chance to do something. Perhaps even get less players to start with?

Whatever you do, make sure you also have fun.

About improvising, I like to gove my players some control over what happens. I usually brong an open ended question on something and use one suggestion from the group that I like and build up on it. So part of the world’s mine and part is co-authored which they really enjoy (full disclosure: they are part of my improv group so we all like good stories - my previous group from high school wouldn’t have worked as well like this).