Try and arrive 20 minutes before your allotted time so you can exchange your prebooked voucher for a real ticket. You can also hand in all your belongings, bags, cameras etc- not hats! That way you are ready to start your tour whenever your two hour slot begins. The galleria is in Villa Borghese so look out for signposts as it's quite a large park and there are other buildings in the park. Sculptures ansd Caravaggio on ground floor, paintings one floor up.
If you own or manage Galleria Borghese, register now for free tools to enhance your listing, attract new reviews, and respond to reviewers.