I think that's a reason to focus MORE on original stuff, honestly. The longer you put off working on it, and the longer you worry about making it good, the more of an obstacle you have to get over when you finally do start working on original stuff. Postponing stuff doesn't always make it easier - sometimes, it makes it seem more difficult and scary. If you get stuck on the idea that it absolutely has to be great, it's going to be difficult to do it at all - perfectionism is something we all have to get over.
You don't have to jump in the deep end with your first project! I mean, I'm drawing an epic story that I will be lucky if it clocks in under 1000 pages - but it's not my first project. I started out doing small oneshots and then slightly longer stuff, and then slightly longer stuff again. You can start doing 5-page oneshots, or 10-page stories. I once did a 7-page story just to practise fight-scenes and panel-layouts.
But if you really want to do fan-comics, when go ahead and do fan-comics! They can be a lot of fun, and they will definitely get more notice for free than original stuff does.