Congressional District Office Internships

Hey, so I found an internship at my local Congresswoman’s district office for the summer (I’m a high school student-rising junior). My question is, are internships like these hard to get, especially for someone my age? The position is open to high school students, and the position is advertised on her website. Are there typically many other high schoolers who are hired?
Furthermore, if I was forced to take a couple of days off because of a family vacation or something like that, would that be allowed/would I have to do the internship for the entire summer (june through end of august)?