This problem has happened to me before. It is caused by not allowing the paint to fully cure. After your first coat, you can recoat once within twenty four hours. After that, you need to wait seven days. If you don't allow this time for the paint to fully cure, it will wrinkle, bubble, and/or crack. You just have to be patient. To fix the problem, let the paint fully cure, then with a fine grit sandpaper, sand down the imperfections and recoat it. You should be fine after that.