Hi, Claire:
Once you have added your cat to your profile as a dog, you'll need to select "cat" from the breed option. Once you've done that, you'll be able to get the appropriate quotes for bookings.
It's going to be more difficult to find a boarding situation for a cat, as most of Rover's sitters board dogs or have dogs of their own. And they may not always be cat friendly. But it can be done!
Using the search function on the Rover website, you can select options like "does not own a dog" (if your cat doesn't like dogs). You can then send messages to sitters that appear in the results and see if they would be willing to board your cat.
If you're interested in giving house sitting or drop-in visits a try, I would highly recommend that for most cats. Rover's sitters are all background checked, and your home is covered by insurance in the event of any damage or misconduct.