Your invention is protected in the sense that it is filed with the US Patent Office for 12 months. Anyone applying for a patent application of the same invention will be behind you in line and you will be first eligible to get a patent. However, you get this protection only if you file a non-provisional patent application before your provisional patent application expires 12 months after its filing. If you don’t file a non-provisional patent app before the provisional patent app expires, the filing date of the provisional patent app disappears and your protection is lost.