Fitting all of the music on one page

I would first try to decrease the MIN system distance as little as possible to make the orphan system end up on page 1. Find it at Style->General...->Page.

And/or decrease stretch (Ctrl+A to select all, then Layout / Decrease Layout Stretch) or reduce overall staff size in Layout / Page Settings. Only reducing system distance or stretch often results in music that is too crowded, but only reducing staff size might make it smaller than you'd like. Finding the right balance is an art.

If I may ask a question...
You wrote:
I recently transposed a piece for the flute, and after I finished it ended up being two pages.

Did the transposition involve a new key signature, needing more room on the staves?
Like from C major to Db major.

I go to page layout -> page settings -> scalings and lower the value slightly. But I also must be careful that everything does not become too small to be legible. Using this method shows me the number of pages, as I adjust the value. As long as it's not too large a change, I can usually decrease the document by at least one page.
For only six measures on the second page, this should work. My default value is 1.764mm....I just decreased to 1.564 mm to allow 5 measures to not be on an additional page on a document on which I am currently working.