Try to avoid the horizontal scrollbar for the moble, as per the standars UX.
In your skin according to the configuration for the foramts for the Grid i.e the responsive breakpoints configured for the grids ,it will render and also as per the setting on the column of the grid i.e primary ,secondary or other.
Please share the sceenshots for these configurations and also for the issue.
Page level Horizontal/vertical scroll auto appears upon screen resize.For Mobile instead of grid use Repeating Dynamic Layout or if still want to use Grid you need to mention primary secondary column .
In mobile Horiontal scroll is not good deisgn as per standrad .