I wrote the following for someone asking about choosing the aero or astro side in school, but trust me, the same applies to internship or even post-graduation work experience.
While you might think of aerospace engineering as a broad topic, it's truly a very specialized focus of mechanical engineering, so don't worry! Any degree will aerospace engineering will have courses in and expose you to the aero and the astro side of the degree. Then as you get into your junior and senior years, you'll be more focused on one over the other and choose a track, but the classes you take as a freshman and sophomore will help to guide you to your true passion. And just because you focus on one DOESN'T mean that you'll be stuck in that realm forever, you'll be able to work in the field on either side because engineering teaches you how to be a critical thinker and a problem solver who can learn and tackle anything. And you can usually take the classes on the other track as electives if you wish, that way you come out as a very well-rounded aero/astro engineer. I hope this helps!