I feel that there should be a simple couple of position coordinates, like {1,0,1,0} to fill up the screen in Size.
I've been looking everywhere, and I've tried lots of solutions in other places.
There is a simple solution that I use to center a gui. I do
local size = script.Parent.Size script.Parent.Position = UDim2.new(.5 - (size.X.Scale / 2), -(size.X.Offset / 2), .5 - (size.Y.Scale / 2), size.Y.Offset / 2)
What this does, is put the X axis to the middle, and subtract half of the size X scale, and the same for the Y axis.
But what you put in your question is different than what you put in the question title. So, to make the frame fill up the screen, do
script.Parent.Position = UDim2.new(0, 0, 0, -200) --to fill up Roblox's top bar thingy. script.Parent.Size = UDim2.new(1, 0, 2, 0)
Hope this helps!!