Congratulations, you made absolutely the right choice, even if the startup is a total failure.
As someone who has worked with many right-out-of-school CS graduates, I'd strongly suggest you pursue a lot of code writing. I'm sure you'll be doing this at the startup. But spend as much time as you can doing it, and learning from errors in production, and in review.
The real thing that CS programs lack is teaching people how to program. I mean that seriously. They focus on theory, but rarely on actual programming. If your startup does not consume absolutely all of the programming energy you have, then work on a cutting edge open source project on the side as well.
If you wish, there are classes in iTunes university, and you can surely peruse the catalog of the university you left, find the classes you would have taken, and buy the books, or comparable (cheaper) books on the same subjects and study them. I've done this in the past, but found that books targeted at practitioners in the field are generally more effective (and at the same cost or less) than those targeted as textbooks. (Back when I was younger, when I'd be going into a new area and wanted to research it, I'd wander into college bookstores looking for things like machine vision, etc.)
The industry oriented books won't have tests and problem sets for you to do... but you don't need them because you're pursuing this knowledge to help you complete some goal, right? For instance, maybe you want to build a robot that can compete in GPS Magellan and you need computer vision expertise for that? (That's what I did.)
When you are excited about a project, you will go and devour what you nee to learn, and you will learn it much more deeply and fundamentally than any class can teach you.
So, find projects and pursue them.