how do I get more clients?

A quick search of Chipstead, even after I adjusted the price filter to be no more than yours, resulted in hundreds of sitters. I'd suggest you don't rely only on rover for clients. You can promote online, use social media, or in print. Introduce yourself to people you meet who may have a future need (people who you meet with pets in the neighborhood, at parks, stores, and pet friendly places) as well as finding out if there's somewhere you can spread the word through your school - past or present. If someone finds you outside of rover, you can choose to book through rover or on your own.