Marie,
It is ALWAYS better to download the PDF file to your computer, and open it from there, before you print, than to try to print from the file while on the internet. For some reason, PDF files do not print accurately when you open it online and print from your web browser. I haven't had any issues with sizing, if I download the file first, then open it on my computer, then select print.
It is always best to check one page to make sure it is accurate, before printing a number of pages. But in most printer settings, you can select the pages you want to print, so you don't have to print your test page again, if it printed at the correct size. I have never had any issues with getting the accurate size, as long as I download the file and open it on my computer first. Also, make sure you have "Actual Size" selected in your printer settings as Helen suggested.
Diane in Colorado Springs