"The bet is on!"
Translation:Die Wette gilt!
No, I think "Die Wette gilt" is a fixed expression, anyway ever since the German tv audience had been hearing that phrase for decades on the show "Wetten, dass...?" (I think it was called "Wanna bet?" in English).
If you can use "Die Wette läuft" at all, it would be to say, "the bet is (already) going on", not "the deal on this bet has been sealed".