To precisely fit your symbols to your plans, Groundplan allows you to rotate the symbols at any angle.
While counting, click the Rotation button (that's between Mode and Style) on the top green toolbar and you will be able to edit the symbol rotation.
You can enter the angle by value or you just use the slider to choose the angle. There is also a preview to show exactly how the symbol will look like before you place it.
You can also click the reset button to bring the symbol back to its original position, and a couple of shortcut buttons to help you rotate the symbol in either clockwise or counter-clockwise direction in 45º degree increments.
You can also use the ALT+E and ALT+R keyboard shortcuts to rotate the symbol in 45º increments.