Programming drum beats: HOW to add extra measures? Help!

Hi all,

New to Cubase AND Mac computers, but loving them!

I have just learned how to open Groove agent, and create an instrument track to create a drum backing track.

Here is my problem-- the new window opens up and gives me a limited amount of measures/time to program-in my drum beats. At the END of the grid, anything else I try to program will show up as a colored block, but no sound comes out. The little vertical line keeps moving left to right, but no sound.

How can I extend my grid outward indefinitely to add the extra time/measure I need to get my drum backing fully programmed? I only have something like 15 seconds available. Is this because I only have the 30 day demo of Cubase Elements 8?

Please help me guys!

Many thanks!