I’m sorry that there was no picture or *.skp file. I hit the enter button and then I saw that my message must be approved first. So I couldn’t edit my message on that time.
Here are the *.skp file and the picture.
It went through for me. The trick to stopping Push/Pull where you want it is to either type the distance after you start the face in the right direction or click on the edge at the end of the travel.
Good luck. You might also consider drawing the flat face with the cutout before making it 3D. It would save you a couple of steps. Or draw the entire opening on the 3D plate and push it through in one step. Just options.
SketchUp has always been good at being easy to learn and having multiple ways to do things, but optimizing the order you do things in, like DaveR said in his post can save a ton of time down the road. Don’t be afraid to try something a different method next time you model something. There is always something new to learn.
It’s a quirk of computer arithmetic. In some number representations it is actually possible to have both positive and negative zero! Which happens depends on the calculations that led to the zero.