The numbers on the spots you've already played represent your highest experience percentage you've gotten on that field, I believe. I could be wrong, but that's what it looks like to me.
You can press the "Manual Timeout" button beside the Combo Timeout meter or you can just go to the store for a couple seconds and it will stop the combo.
 "GemCraft Labyrinth"){kind=icon}
 "Epic Combo!"){kind=icon}
 "ShellShock Live"){kind=icon}