I haven't had experience with Noteworthy, but in other notation programs, you typically chose the number of measures in your score at the outset(16, 32, 64, etc) if you need more, you have to use a command of some sort to add measures--so just check your manual to find how to add measures.

It is usually less cumbersome to work with a score in sections, anyway, and I tend to make files that include only as many measures as will fit on a page--often only four or eight measures, depending on how many parts there are--I know that many people always keep it to four, right up until the parts are extracted.