Hallo:o
this is my first Game make with Blender
i working on the next Game.
Name of the Game is Flappyball
Very nice, especially for a first game! Having a high score screen would be nice, but might be a bit difficult yet. I don’t see to many high score screen around. 
a highscore screen shouldnt be difficult:
in a python script you’d just say: if the ball is at the edge of the screen ( he already has made some way of detecting this since the game restarts at that moment), go to another scene, where you have made a highscore table with some variable text and stuff.