OK, for others who are similarly confused -- will share my experience.
I went onto the Scrovegni Chapel website to buy the 48H Padova Card (which includes transit & museum entrances).
I got to the on-line purchase page.
I selected 2 Padova Cards. I got a message that read:
On the Internet the card should be selected together with the corresponding ticket for the Scrovegni Chapel. In the same way, it's not possible to purchase such a ticket without its corresponding card
So I tried to enter in 2 Cards AND 2 Entrances -- nope, didn't like that EITHER.
FINALLY I figured out that farther down the page there is an option to pay 1Euro per person for your entrance reservation -- chose the Padova Card + the Reservation = BINGO!
It was especially frustrating because on the day/time I want to go there were only 5 spots left and there are two of us --- I could hear the clock ticking.
Total cost was 16E + 1E = 17E currently = USD/CDN$22.
Since I'm arv/dep from the train station & want to see a few of the museums (including the Scrovegni Chapel which all by itself is 13E) I think this is actually a good deal as it provides unlimited public transportation, access to the Scrovegni Chapel & entrance to 9 other sites.
Hope this helps others!