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 >.>