Especially when exercising, it is easy to sweat when exercising, and it will not be so boring with bare arms. Many men don't wear tops when exercising.
But it is rare to go shirtless in the classroom or other places, but it doesn't matter. After all, it's normal for men to go shirtless. It will be very hot after exercise. If you want to go back to the classroom, there is no problem with bare arms.
Don't care too much about other people's eyes. It doesn't matter if other girls feel bad. There are so many people with bare arms in the street that they don't care much. It is only because they know you that they express their bad feelings to you. Don't care what they think, just be comfortable.