Does the page look correct when you do a Print Preview on the box and whisker plots (right mouse click in b&w plot window)? It should be WYSIWYG. I’ve printed many b&w plots on a range of laser and inkjet printers and have had no problems.
How many groups and variables do you have, and what printer are you using? Numbers shouldn’t matter but knowing this and the printer, I may be able to try and reproduce the situation.