Problem with columns

Hi,

in one section, I created three columns with the plugin Lightweight Grid Columns,
with these parameters:

[lgc_column grid="50" tablet_grid="50" mobile_grid="100" last="false"] FIRST COLUMN CONTENT[/lgc_column]
[lgc_column grid="50" tablet_grid="50" mobile_grid="100" last="false"] SECOND COLUMN CONTENT[/lgc_column]
[lgc_column grid="50" tablet_grid="50" mobile_grid="100" last="true"] THIRD COLUMN CONTENT[/lgc_column]

The problem is that the third column does not remain on the same line but goes under the first column.

At this link a screenshot with the problem : https://www23.zippyshare.com/i/BK9Z3kPg/377124/screenshot.png

What should I do to get the three columns on the same line?

Thanks

Giuseppe