Looks good

.
Maybe this will work for you, since your square isn't completely square and the lines you probably want north aren't completly north.
In a lot of drawing programs (at least those who I encountered) you can use the SHIFT-button for various things.
An example for Paint.
- While drawing with the rectangle tool, holding SHIFT results in a square.
- While drawing with the line tool, holding SHIFT results in one the following lines (depending in what direction you pull the cursor while drawing the line):
North, East, South, West and those exactly inbetween (45 degree angles).
- Those are the things I use most, but there are various other things you can do with SHIFT combined with the tools, you might wanna play around with them.
Edit: In Inkscape it seems to be CTRL.
Hope this helps you out for creating diagrams in the future!