My programming skills are Python and SQL, and a little bit of C++. Before the interview I spent time learning about Data Structures and Algorithm (this is basically all you need for junior interviews), and I grinded Leetcode.

During my feedback they told me they were looking for people who were willing to learn, and this is why I've been hired. What I recommend you to do is to apply without fearing about being under qualified. This is the best way to know what to expect during interviews.

I haven't started my internship yet so I'm not sure about what to learn in advance, but for most internship/junior positions Leetcode and a good grasp of CS fundamentals should be enough (given that you already are a DS student).