Does rejecting a summer program look bad?

I’m a rising junior in HS and have started looking into internships/summer research programs/apprenticeships for next summer. Because so many programs at universities are incredibly selective, I’m worried I won’t get into a program if I only apply to one.

I’m now considering applying to several–but for me that raises the question, “If I get into more than one, does turning a program down look bad? And if it comes to that, how do I turn down an acceptance?”
I feel like for a lot of these super selective programs, they have a set number of students they’re expecting and it seems like the organization might see turning down such a good opportunity as rude?

I’ve never applied to any of these research programs before so I’m not sure what the process of application=>acceptance=>attendance is like.

I also don’t want to imply that I think I’ll get into even one of these; I think I’m a relatively-mediocre-student-kind-of. But the chance that I might be lucky enough to be accepted makes me nervous about the prospect of having to turn a program down.

Lastly: I’m sorry if this post is in the wrong forum; I’ve been lurking on this website for awhile but only just created an account–I haven’t yet found my way around everything.

bump!

How would anyone know you turned them down?

Or are you saying if you turn down a program at College X, will College X not admit you?
I am not sure that the people who run the program have anything to do with Admissions.

Just find the right program for you and don’t worry about other programs you don’t go to.