"Just quit my dead end 9-5 corporate job"
Should you be worried? I think you asked this question a bit late. You probably planned it that way. The answer doesn't really matter because worrying won't do anything to help you out.
Have a plan B. A big part of plan B is to work the networks you have to keep them from getting stale and expand into new networks. Every contact you have in your virtual Rolodex is a potential glass covering you can break in the event of an emergency. Those contacts will also help with your startup.
Another part of plan B is to keep an eye for where you would be going if the startup doesn't work out. If you are going to do freelance work, then where are you going to be looking for that work? Perhaps you should be sniffing around in those areas just in case (keep an eye out for prospects, make more connections, talk to people, etc.)
Three months doesn't give you a lot of wiggle room. A lot of this depends on your situation also. Three months living expenses could be something like $10.50 if you are living in your mothers basement. If you have a good number of expenses then taking care of all those with Freelancing will likely take you at least a couple of months unless you are well connected. You might try taking on small gigs here and there to extend your three months cushion and get a taste of doing client work.
Keep in mind that freelancing is yet another business. It's a hole that you get sucked into and your startup may take a back seat at times.
Good luck. Or, in the zombie scenario, Lock and Load!