I usually run huge resolutions because I'm a weirdo, but I'm assuming your question/problem to mean that the cpsketcher work window is too small for you to use it adequately.
Well, changing your desktop resolution should help considerably (Which I've noted you've done)
The other thing you can do to get really accurate placement is to turn on the 'snap to grid' option, and then adjust the grid size. And don't forget that you don't need to make reeeeally tiny squares if you don't need to... For instance, I've set the grid out to 3 inches for some odd placements, and 10 inches for others.
As to an actual 'zoom in' function, I don't believe there is one on CPsketcher, but I hope those ideas help you find a work-around!