I would take 1 week and observe the T-Rex from inside the hut. Make small, but safe, movements.

After determining that I will be unable to kill the T-Rex I will inform the person running the game that I can not kill the T-Rex and would like to forfeit.

The person running the game would protest, but eventually realize I am not going on provide any further entertainment.

They'd bring in the professionals to corral the T-Rex and contain him.

Those professionals? A secret team I've hired. My forfeit? I had my fingers crossed.

With the T-Rex contained and drugged, I stab the T-Rex.

The team and I split the winnings. Credits roll.