A bike is a tool. Tools wear. Tools get dinged and tools get lost, stolen or even broken. Enjoy riding the bike and don't worry about the dings. If you must worry, and if it's a road bike, then yes, a protective film is a good option. If it's a mountain bike, a cut up old tire taped under the down tube and bottom bracket will protect that area pretty well but looks kinda ugly....or cool as heck depending on who you are as a rider!