Im ready to fly my GSCALEPLANES Corsair , Im making sure everything is absolutelly perfect, I heard from someone who had flutter on this plane, and I have found that the elevators in the plane have a little play.

Transmitter and reciever on I can move them a little, not the same with rudder or Ailerons.
Is it dangerous to fly it like this? can this cause flutter?

Any gap or loose feeling in the controls will cause flutter. If you are using CA hinges and you have up and down movement in the surface and a gap you will get a flutter. simple fix is to mono-coat or tape the gaps to prevent a air flow which causes flutter or to install pinned hinges when putting them together. I use pinned and make sure I have NO gap between the surfaces.

Just to add another "Yes" vote on tight linkages and gap sealing...

This is REALLY important. Tape is a good, simple way to seal gaps, and there are others, but this is one of the primary things you can do to reduce or even eliminate flutter. And, as a bonus, your model will be more responsive.

Please explain me how to do this.
I just put tape over the elevator controls and will fix the problem?

Sealing the hinge line is a very good idea to prevent flutter, but it won't help your loose linkage any.

First find out where the looseness is coming from. Is it from the long pushrod flexing too much? If so, you might need to stiffen them up a little. Wooden ones can be stiffen up very nicely by laying on carbon fibre tape with CA. Otherwise you may need to add midspan constraints to limit the amount of flexing.

If it is from loose fittings on the servo or control horns, you need to redo or reposition to get rid of the looseness. I have seen control surfaces flutter from loose linkages with the plane sitting on the ground at engine full throttle - without any aerodynamic load on it.

Definitely fix it.

You have to make the tape into a hinge also. Open the elev as wide as it will go, insert the tape to the bottom of the slot, it will look like a V when inserted and the adhesive takes hold the tape is now a sealer and part of the hinges. Now you have no air flow between the 2 pieces so no flutter.