from buffalo ny: you could always paint a variation of the original
color deliberately on the third wall. maybe a third color like a tan?
or mix your leftover paint in with the next gallon of same color and
you will have a uniform color with some leftover touchup paint.
depending on the condition and type of wall and climate etc, as in
buffalo, you should have normally cleaned wall, applied primer first,
then usually 2 color coats will do it. mix 2 x 1 gallons together for
color uniformity before applying. to save cleanup time we use dollar
store brushes and discard at day's end. we always use a BIN or KILLZ
primer appropriate for your task and follow its label directions
carefully. when painting with a brighter worklight you will catch the
goofs easier than under general normal lighting. daytime painting may
be easier if the room features windows.when all else fails buy a giant
bulletin board for the last wall and paint around it!

Jason wrote:
After 2 days of painting my office, this is absolutely driving me
insane!

I had a gallon of paint mixed at Lowes, and figured that a gallon would
be enough to do 3 walls. Well, I didn't think that I would need 3
coats! It's called "Praline Cake," which is a brown/yellow color
(American Traditions, Historic series).

Well, it's all done except for the 3rd coat on the final wall, and a
few minor touch-ups in the corners. I have just enough paint left that
I might be able to fill the roller one more time, but I'm worried that
this won't be enough. What's worse is that if I go back for more, I
have to buy a full gallon ($20+), and there's no guarantee that it will
be a perfect match for the rest of the room.

So... any tips on stretching this last fraction of paint to make it
last for the entire wall?

TIA,

Jason