Yeah , the "sticky" walls weren't intentional :v . To fix it I need to make the player friction zero and simulate it myself through the code, so he won't stick to the walls but also won't slide when on the ground.
For those wondering, the first level is kind of a semi-tutorial for movement and shooting. If you throw the ball a couple of times or if it lands out of you reach, the next level will be loaded. (You throw with Left Mouse Button)