Yes. You do have a Constitutional right to be out at school if you want to be.
As long as you are being your true self and it is not physically hurting or harming anyone, then you are well in your right to express yourself as you see fit.
In Tinker v. Des Moines, over 40 years ago, the U.S. Supreme Court ruled that students don’t “shed their constitutional rights to freedom of speech at the schoolhouse gate.” The only time a school can legally restrict a student's speech is when it causes significant disruption in the classroom. And while school often use disruption as an excuse to censor student speech, there are clear legal guidelines about what disruption really is. It is not just whenever a school administrator says something is disruptive. For example, yelling "I'm gay!" in the middle of English class isn't okay, but talking about being gay with other students between classes or at lunch is. Nor is your speech disruptive just because someone else might not like it. And if your school's dress code allows other students to wear t-shirts about their beliefs, then it's illegal for them to ask you to take off your t-shirt just because it has a rainbow or say something about gay pride.