If it's a button that comes with InDesign, it consists of two layers. Make sure you've put the word on the top layer.
Check your button rollover states - you may need to copy and paste the submit word into the rollover state.
Ensure you delete the default button style and replace it with a Mailto action.
By the way, you seem to be using the radio button shape for tick boxes. I suggest you use square tick boxes for multI-tick choices and round radio buttons when these's only one choice.