Hi Amanda -
The Roma pass will not help you at the Vatican: they don't accept that pass. It many not help you at the Borghese as well as you must have a reservation - even with the pass - and my guess is that all time slots may be filled at this late date. If you plan on using the pass at the Borghese, you must call them for reservations. From the pass' website:
"For the Borghese Gallery and Palazzo Valentini (Domus Romane), booking is required also for Roma Pass and/or Roma Pass 48 hours holders. Reservations are not required for any other museums, though it is highly recommended that school or tourist groups make reservations, in order to facilitate entry to museums.
For reservations to the Borghese Gallery and/or Domus Romane/Palazzo Valentini, please call +39 06 32810 (open Monday to Friday, 9:00 am to 6:00 pm – Saturdays, 9:00 am to 1:00 pm). Bookings can be made directly from the visitor’s home country, even before purchasing the card. Please note: it is not possible to make an online reservation without prepaying the ticket. If you intend to visit the museum / site with your Roma Pass or Roma Pass 48 hours, you must make your reservation on the phone, by calling +39 0632810."
They'll tell you over the phone if they're sold out.
So if you won't be able to use it for the Borghese, the only other attraction on your list that applies is the Colosseum, and I wouldn't buy a pass just for that. Tickets to the Colosseum/Forum/Palatine (one ticket covers all three) can be pre-ordered here:
http://www.coopculture.it/en/colosseo-e-shop.cfm
I wouldn't buy it for the transportation piece either as central Rome just isn't that big. You can easily buy individual transport tickets for the few times you may want to jump the metro or a bus. The trick is to look at what the pass covers, make a list of the things which interest you and what individual entry fees to those would cost. Add those numbers up and compare it to the price of the pass.
A lot of attractions will be closed on May 1st but we've chatted about some other things to do on this thread:
https://community.ricksteves.com/travel-forum/italy/rome-on-may-day-2015