If your answer was given  in the bounty period and it has earned 2 upvotes but it was not accepted, then after the bounty period has ended + 24 hours, you will receive half of the bounty.

If you did not receive more than 2 upvotes, then the bounty will not be awarded.

More info about the bounty system can be found:

http://meta.stackoverflow.com/questions/16065/how-does-the-bounty-system-work