If it didn't penetrate the skin you should be fine. I haven't heard of people getting tetanus from superficial burns. Tetanus isn't caused by rust, the bacteria thrives in low-oxygen environments like wounds (punctures/fairly deep ones).
I'm not a medical professional though...if you're really concerned about it check webmd or see a GP for more information. Have you been vaccinated for it in the last decade? That is the best prevention.