Hello Marcusandrew,
Square itself is PCI compliant, they don’t require account holders to validate PCI compliance. Merchants who use Square for all storage, processing, and transmission of payment card data do not need to validate PCI compliance for those transactions. Bottom line, you are covered for both selling online and in person. Additionally as part of their compliance policy, you should see that your website URL begins with "https" and in your web browser's address line, you should see a Lock symbol, if you click on that you view the details of your Security Certificate. This tells visitors that your website is secure. There is more info here.
