When I export a score to PDF in landscape layout, it saves as portrait instead but cuts half off! Help?

Hi, quite new to Musescore. I've used it to write out a few simple pupil parts for teaching that I need in landscape page format. When I export it to PDF (I need it for a big overhead projector in school, so Musescore file not suitable) it saves as portrait instead and cuts off half the document! Any ideas? I've got round it by saving it as an image file instead which works as landscape, but I'd prefer to use PDF. Thanks.