Lightning Spell Glitch ?

I have a script that can launch a Lightning by hand to the desired place, but there is a problem in the vector that will position it in a certain position of the map.

how can I fix?

The script:

math.randomseed(tick())

function lightning(startPos,endPos,details)

    local mag = (startPos-endPos).magnitude
    local step = details.Step
    local waitTime = details.WaitTime

    local lightningModel = Instance.new("Model" , workspace)
    lightningModel.Name = "Lightning"

    local lastStart = startPos
    local debugMode = details.DebugMode
    local lightningEnd = endPos

    for i = 1,mag,mag/step do
        print(i)
        if waitTime > 0 then
            wait(waitTime)
        end
        local newEnd = endPos*Vector3.new(math.random(-2*mag/5,2*mag/5),math.random(-2*mag/5,2*mag/5),0)
        if i+(mag/step) == mag then
            print("LAST ONE")
            newEnd = endPos
        end
        local ray = Ray.new(lastStart,(newEnd-lastStart).unit*(mag/step))
        local hit,rayEnd = workspace:FindPartOnRay(ray,(lightningModel))

        local currentMag = (lastStart-rayEnd).magnitude
        local part = Instance.new("Part")
        part.Anchored = true
        part.CanCollide = false
        part.TopSurface = "Smooth"
        part.BottomSurface = "Smooth"
        part.FormFactor = "Custom"

        part.BrickColor = BrickColor.new(details.Color)
        part.Material = details.Material
        part.Transparency = details.Transparency

        part.Size = Vector3.new(.2,.2,currentMag)
        part.CFrame = CFrame.new(lastStart , rayEnd)*CFrame.new(0,0,-currentMag/2)
        part.Parent = lightningModel

        lastStart = rayEnd

        if debugMode then

        local p = Instance.new("Part")
        p.FormFactor = "Custom"
        p.Size = Vector3.new(.2,.2,.2)
        p.Anchored = true
        p.Material = "Neon"
        p.Position = rayEnd
        end

        lightningEnd = rayEnd

    end
    return lightningModel,lightningEnd
end

return lightning

Full module >.>