All you can do is watch him closely for awhile. If there is anything off about his movement, he should probably get an xray.

If he's been very cold (and it's not too late) it's a good idea to warm him back up slowly.

Well, 3 feet isn't too bad of a distance; I mean, it's not something you'd want to happen, but I think he could be fine. One of my geckos, Dizzy, one fell five feet from my desk to the floor, and she was perfectly fine. (Well, as fine as any gecko with mental problems could be.) All the same, I agree with Aimee; keep a close eye on him, and DON"T try to feed him any time soon. Let his body recover from the shock. The fact that there was a soft carpet at the end of the 3 feet drop is a good thing; it means there is less liklihood that he was seriously injured. Is he walking normally? Lick response is normal? He's not shaky or erratic when walking?

He  seems to be fine. I am gonna feed him tonight. He has been staying in his cool hide all day. 

Geckos are surprisingly resilient critters,I've had a Leo fall about 5 ft with absolutely no ill effects (managed to scale a cactus,then somehow climb onto the light fixture,then up and over the cage edge,then down from there..cage has since been reconfigured to prevent a recurrence). I've seen crested and gargoyle babies miss a landing on ill-advised jumps,and fall a couple feet countless times. mainly from the kids holding them,which led to the "gecko in hand,butt on floor or chair rule"...mainly to discourage wandering while holding geckos.

just keep an eye on it; if it starts doing anything abnormal,check into seeing a vet.

It looks like you have nothing to worry about, then.  Like Jetfire said, you'd be absolutely amazed at what geckos can survive; I have a few stories about leo survival that don't even seem possible.