Missy, since it is relatively fresh, you might try Steve's method first, with one limitation. Check the can, but it probably is a latex or acrylic latex paint. And ammonia does not cost much. Start on a small area nearest to the drain in your floor.
It probably has been too long by now so the next step would be to use an environmentally safe stripper like Citristrip. Glob the Citristrip on with a cheap, wooden handled, natural bristle brush, and let it work for 12 to 24 hours. Leave the garage door open while it is working and keep kids and pets away. Be sure that you read and follow all the usage and safety directions on the bottle and leave the car outside while this is going on. Check at www.citristrip.com and you can see a video of the process. When the surface looks like the ready-to-strip surface in the video, remove the paint/stripper goo with a putty knife. It may take several applications with the paint thickness that you have. Your home center should carry what you need for this.