If you're an in-state student, there is an extremely, extremely high chance that you will not be the only one coming to UMass from your high school. At my high school in Framingham, Mass., there were people who looked down on and actually refused to apply to UMass simply because of how popular of an option it is. Coming from a class of more than 500 students, I was among 40+ students leaving my high school to come to UMass. I will admit that it's a rare occasion for me to go an entire weekday without seeing at least one person from my high school while walking to or from classes, but I'd like to break the stigma that this is a bad thing!
While it may seem counterintuitive to the college process of diversifying your interests and meeting new people, I don't think there is anything wrong with keeping in touch with high school friends who also go to UMass. It took me all of my first semester for things to really "click" in terms of making solid friendships with people on my floor or in my classes, so I leaned on Libby, my close friend from high-school, and formed a friend group of us and our roommates, Casey and Mary Kate. As I got to know Casey and Mary Kate, it was really nice to have a familiar face to go through the first-year experience with at the same time.
What I'm trying to say is that there is no reason to feel ashamed about sticking to people from home for a bit while you get your bearings during your first weeks or months at UMass. Don't feel like you have to ignore people you knew in high school just because you're in college now. It can be really nice to see a friendly face on campus even if it's just to smile and say "Hi" in passing, so embrace it!