PEB, I'm no expert with CC3, however, I am assuming you are using the New Page Wizard in order to place your Hex Grid, well the second window of the New Page Wizard, right before you get to set your grid is where you determine your base map dimension.

If you left it in its default setting, your map is 800 x 1000 or 8" x 10".

Note CC3 is a vector application so you are able to rescale easily enough - though I don't know how to do this myself.

What I'd do, since you're a newbie, is go back to the New Page Wizard and at the dimensions menu, set the dimensions what you want - ie for a 24 x 36 map, you must set to 3600 wide x 2400 tall.

Does this help?