First booking got canceled. Scam?

When new clients perform a search and select a sitter and then create a booking request the Rover platform automatically sends the booking to several sitters unless the client unchecks the box which most don't. So you weren't the first sitter selected and so they canceled the booking and probably place it with their sitter of choice.

Note: NEVER accept a booking until after you have had at least a few texts between yourself and the client and I highly recommend a meet and greet also. Best of luck in the future.