You're at the start of your PhD and still defining your research topic, so you shouldn't be alarmed that you haven't figured it out yet.
It's almost inevitable that your supervisors will find problems at this stage. Their feedback should help you focus your ideas, close of less productive research questions, and place tighter parameters on your work. Students commonly end up examining a very small area of their proposed topic.
It sounds like you're experiencing the same anxieties the overwhelming majority of PhD students feel early on, which is not to downplay how you feel. Importantly, you're also thinking about your work critically, and the ability to solve problems you identify is an essential skill for PhD research.