why is gas coming out of primer button when button is pushed?

Sears B&S 6.75hp self-propelled mower. Fine Sunday...left it with 1/2 tank gas. Strong gasoline smell in garage since then. Tuesday no gas in it at all, but no sign of gas on floor or mower either. Filled tank, pushed primer button and gas spurted out of little hole in the button. I was afraid to try to start it (I am senior lady trying to learn to do these things since my husband passed away in Jan.). The Sears repair center is far from my house, mower is only 1 year old....anything I can check for before taking it into the shop?