This is a pretty lackluster game -- you could do a lot more with this game. This is a good concept, though.
Three minutes is not enough to do everything (well, mostly for score). A time extension feature does not hurt. Oh well.
The main problem with this game is really the luck element to this game -- whenever you make even one move in the heat of the round, you never know where whatever gem will be placed, and the game may screw you over by randomly placing a wrong gem where you least expect it. The randomness aspect of the game should be ousted. It is a good idea to include a "warning" type feature that shows the ghosts of new gems that will be placed as well as where, so that the person can plan things out and develop a strategy accordingly.