Why might my Speed Boost script throw this error?

So here's the rundown.

My vehicles need a script to boost their speed for a short period of time (while shift is held down)

I'm sure I've ruined my script by now trying to fix it, but the error I inevitably get is: line 28: ')' expected (to close '(' at line 20) near 'while'

---Or along the same premise. Missing '('

Warning for the faint of heart: I'm a little new to scripting and so I put a lot of unnecessary precautions.

function check()




script.Parent.Touched:connect(function(hit)

    mouse = hit.Parent:FindFirstChild("Humanoid")


    if not mouse then return end
        mouse:GetMouse(KeyDown:connect(function(key)
            while KeyDown:Connect()==true do
            if key == "48" then
                if given==true then return end
            else boost()
        end
    end

            mouse:GetMouse()KeyUp:connect(function(key)
                    if key == ("48") then
                        if given==false then return end
                    else cut()  
        end
    end
end

while true do
    wait()
    check()
end