It doesn't rule out AOS at all, but you will have to work harder to prove that your marriage is real. Normally USCIS likes big weddings because they show that you thought about and planned getting married, it was a significant "event" in your life that you wanted to celebrate (not as common with sham marriages), and your family and friends support you as a couple. Of course, people have small weddings for lots of reasons, so it's not the end of the world if you did, just be prepared for questions.
When you go for your AOS interview, you should have as much evidence as possible to show that your relationship is real -the most important thing seems to be comingling of finances, like joint bank accounts, bills, and ownership documents (house, car, etc.) You should also be prepared to answer questions about the home you share together - sometimes trivial things like "what color is the laundry basket" and "what's the name of your landlord."
You will probably be asked who attended your wedding, and if no family attended, you might be asked for a reason why. You may be asked if you've met each other families, and if you can name members of your spouse's family. Again, this is because USCIS sees family support/involvement in your marriage as a good sign that the relationship is real.
If your marriage is real, you should be fine. Many, many people get married in courthouse weddings. Just be prepared for a couple of extra questions, and make sure you've got all your evidence together and organized before your interview.
