Prop Betting Procedure Question

[NLSoldier]

Please consider the following scenario.

We have 2 people. Person A and person B. On day 1, person A and person B agree to bet on a task that person A is to complete on day 3. If person A completes the task by a specified point in time on day 3, he wins the bet. If he fails to complete the task, person B wins the bet. The bet is agreed upon.

On day 2, person A comes to person B and says he wants to cancel the bet. He cites the fact that no circumstances have changed since the time the bet was agreed on. Person B says he does not want to cancel the bet, and argues that the fact that person A now wants to cancel is a change of circumstances in itself.

Does person A have the right to cancel the bet and not pay person B any money?