Tweening Negative sized GUI objects failing?

Whats up, so i'm working on a loading screen and this is currently what occurs;

https://gyazo.com/05ce4919e35226c5ae558ecd259a7344

Current script for the backdrop being;

local bg = script.Parent.Parent.Backdrop

if bg.Size.Y.Offset == 5 then
bg:TweenSize(UDim2.new(0, 125,0,bg.Size.Y.Offset-45), 'InOut', 'Quad',0.5, true)

elseif bg.Size.Y.Offset <= -50 then
bg:TweenSize(UDim2.new(0, 125,0,bg.Size.Y.Offset-50), 'InOut', 'Quad',0.5, true)

elseif bg.Size.Y.Offset <= -200 then
bg:TweenSize(UDim2.new(0,125,0,5),'InOut','Quad', 0.5, true)
bg:TweenPosition(UDim2.new(0.5, -62,0, 0),'InOut','Quad',0.5,true)
wait(0.5)
bg:TweenSize(UDim2.new(0,5,0,5),'InOut','Quad',0.5, true)
wait(0.45)
bg.Visible = false
bg.Position = UDim2.new(0.5, -62,0.554, 0)
bg:TweenSize(UDim2.new(0, 125,0, 5),'InOut','Quad',0.5,true)

end

What I'm attempting is to detect the size and increase by a value, because it'll work in a loop, any suggestions?

No errors printed but if I go into explorer and after the first action, the size resets to 0, 125, 0, 5 (Default size) and presents this on the UI !