Hi, hope I'm not too late?
2 days is just fine, you'll see the main sights.......
Rialto Bridge
Bridge of Sighs
San Marco Square and go inside the Basillica
There is also a really tall bell tower at this square where you can get a lift to the top and see the most amazing view.
Other than that eat, drink and soak it up baby, it's fab!
Here is my thread from when I went
Ciao Bella - Venice..........Lurvely