gui position is changing with different screen size, how do I "lock" GUI to a certain position?

So I just published my game on roblox and me and my friend tested it out. But when he is in game, the GUI position changes. And I think it is because the difference in screen size. I use scale, do I have to use offset?

If you put offset to 0, it will "lock" the gui to a certain position. There are some plugins out there that might be able to help.