ChatGPT is a web app (you can access it in your browser) designed specifically for chatbot applications—and optimized for dialogue. It relies on GPT-3 to produce text, like explaining code or writing poems. GPT-3, on the other hand, is a language model, not an app.
So, yes, you are right, ChatGPT is an interface, through which you are accessing the power/ capabilities of GPT-3