RE:Increasing width.

You can set the column width through width parameter like this 

columns:{

a!gridColumn(
label:"First Name",
width: "2X"
)...

You can set the column width through width parameter like this 

columns:{

a!gridColumn(
label:"First Name",
width: "2X"
)...

but I have used readonly grid.

You can use  width and weight property in editable grid also

columnConfigs: {
a!gridLayoutColumnConfig(
width: "DISTRIBUTE",
weight:3 ),
a!gridLayoutColumnConfig(
width: "DISTRIBUTE",
weight:2 )

}

Weight Determines how wide distributed columns are in relation to each other. Valid values: integers from 1 (default) to 10

yes I have given weight as 10 itself, but the thing is that same interface having more number of columns at application level but in dashboard level less no of columns. for rest of the columns I have given narrow.

JS0001 said:

but I have used readonly grid

The grid in your screenshot (i.e. a!gridLayout()) is the Editable Grid.  Read-only, aka "paging" grid, is a!gridField().

Yes sorry,it is working as a read only.i have tried with conditions like if it is in dashboard then with width and weight as distribute and 10 and aslo for non dashboard thing. I  am not getting how else I can do?

The "weight" values for columns only adjusts their relative widths compared to other columns.  The only thing you can really do here is to play around with setting different weights to different columns and figuring out what works best.  On grids with lots of columns, there will always be squeezing of individual columns regardless of what weightings you set.