I need to fix bugs on this stamina bar. Any Comments?

local userInput = game:GetService("UserInputService")

local players = game:GetService("Players")

local sprintSpeed = 25

local walkSpeed = 16

local maxSprint = 10 local staminaCount = maxSprint

local player = players.LocalPlayer

local function beginSprint(input, gameProcessed)

if not gameProcessed then        

    if input.UserInputType == Enum.UserInputType.Keyboard then

        local keycode = input.KeyCode

        if keycode == Enum.KeyCode.LeftShift then 

            player.Character.Humanoid.WalkSpeed = sprintSpeed
            if staminaCount > 0 then
                repeat
                    wait(.5)
                    staminaCount -= .5
                    script.Parent.Size = UDim2.new(staminaCount/maxSprint,0,.16,1)
                until
                staminaCount <= 0
                if staminaCount <= 0 then
                    player.Character.Humanoid.WalkSpeed = walkSpeed
                    repeat
                        wait(.5)
                        staminaCount += .5
                        script.Parent.Size = UDim2.new(staminaCount/maxSprint,0,.16,0)
                    until
                    staminaCount == 10
                end

            end

        end

    end

end

end

local function endSprint(input, gameProcessed)

if not gameProcessed then

    if input.UserInputType == Enum.UserInputType.Keyboard then

        local keycode = input.KeyCode

        if keycode == Enum.KeyCode.LeftShift then

            player.Character.Humanoid.WalkSpeed = walkSpeed
            repeat
                wait(.5)
                staminaCount += .5
            until
            staminaCount == 10

        end

    end

end

end

userInput.InputBegan:Connect(beginSprint)

userInput.InputEnded:Connect(endSprint)

i need help fixing things like the choppyness of it, when it fills up you cant start using the sprint again to make it go back down and when it fills up all the way it doesnt stop when the bar is full. any help?