How come this script wont work?(Lines 12-15) wont work

This is my damage script to my fire ball tool and it works with the damage but when I try to add it so that if the Player kills another person their Exp stat in the leader board raises the damage still works but the Exp stat in leader board doesn't raise. I used the Variable PlayerName to find the name of the Player in the Players Folder so I can access the player

PlayerName = script.Parent.Parent.Parent.Name

function onDamage(Part)
    if Part.Parent:FindFirstChild("Humanoid") ~= nil and Part.Parent.Name ~= "script.Parent.Name" then
        script.Disabled = true
        f = Instance.new("Fire", Part)
        for i = 1,25 do
            f.Size = f.Size +0.25
            Part.Parent.Humanoid.Health = Part.Parent.Humanoid.Health -1
            wait(0.05)
        end
        Part.Parent.Humanoid.Sit = true
        if Part.Parent.Humanoid.Health <= 0 then
            game.Players.PlayerName.leaderstats.Exp = game.Players.PlayerName.leaderstats.Exp +1
            end
        f:remove()
        script.Parent:remove()
    end
    wait(0.025)
end

script.Parent.Touched:connect(onDamage)