If there are fewer columns and you choose to fill 100%, the Grid will shrink itself to fill the screen. If there are more columns horizontal scroll bar appears, which is an expected behavior. as an alternative, if you want all columns to be viewed in the single screen without any scroll bar, you need to add the width of each column size based on the viewable content.
Else based on the screen resolution you can set the columns to limited providing the priority to each and every column configuration.
For 18-20 columns, If screen size is 1920*1080 or more, result should fit to screen.
When screen size is less than above mentioned, result should be fit to screen but with horizontal scrollbar to see hidden columns. As of now, due to this, scrollbar is coming on browser and whole portal size is getting increased which is not acceptable. No columns should be eliminated based on priority, but scrollbar should come for small screen desktops.