What to do in Rome, Italy?

My mom and sister just came back from their vacation (they took a cruise).

We will be staying here.

I just booked our stay from May 25 - May 28.

From what my mom tells me, this hotel is right in the middle of everything.

We can easily walk out the front doors and have cafes, restaurants, shops, etc. within walking distance.

We opted to go with a Classic Double room versus one of the "Economy" rooms. For just a little bit more, you get a larger room, more amenities, etc.

It includes free breakfast and WI-FI.

I'm not exactly sure what we should do.

Other than eat risotto, pizza, pasta and gelato. And drink coffee. And wine. Lots of wine.

I would love to see the Colosseum, just to see the grandiose-ness of it. I'm excited to see the rich architectural history that there is in Italy. We are going at peak time (summer) so we'll see how hot/humid it is and how busy it'll be.

I want to go to St. Peter's Square.

We get there on a Monday morning and then leave for Santorini Thursday at noon. My mom swears that's enough time in Rome.

I hope she's right!

Any ideas for where we absolutely need to go? If anyone is out there reading this (anyone?) let me know!