The Frustration of Map-Making (Or Established Settings vs. Homebrew)

I'm really hit or miss when it comes to making maps. My method can basically be condensed into "Start drawing and see where it takes you." If I don't like the way something looks, I erase and redraw and generally, that's worked out for me. But with the deadlines for beginning both of my D&D campaigns (Library 4th Ed and college friends S&W), I have become incredibly frustrated at my inconsistency.

I've been working on my campaign worlds for both of these games: the aforementioned Discworldian darkly humorous fantasy world and a more console RPG-inspired one for the 4th Edition game. Progress has been slow going on the library game. I've drawn a handful of maps that have yet to fit my specifications and with my first week in library school starting today, I've been looking more and more at the published campaign setting of Eberron. I'm a huge fan of Eberron and its pulpy, high adventure feel. I like the appeal of an established campaign setting as a ready hook for adventures and inspiration, not to mention that I appreciate that Eberron is a world definitely inspired by the kind of games that these kids have already experienced. But I'm afraid that it will be an overwhelming prospect, with dozens of character options and the framework of an entire world to lay out in broad strokes.

Right now, I'm kind of stuck between a rock and a hard place. I'm overwhelmed by the prospect of an established campaign world, but my attempts to jumpstart my own setting have been lackluster at best. I just feel that if I can get one good continent map out, the whole Library D&D world will fall into place. But right now, I'm just not sure if I have the time.