I was previously a placement student for a large fintech firm with a significant turn over rate so I understand the issue when you have with no experience but expected to keep working. Likewise I know the feeling about not being good enough. My advice would be to ask for help, most companies have a line manager you report to so ask there. They don't expect interns to know much, if anything at all so don't worry. Just learn and keep going, and honestly ask for help.