What should I wear to my first track practice when the weather is a high of 50 degrees?

Keep in mind I cannot wear shorts or capris, school policy. I can only wear sweatpants...but should i wear a t shirt? or a sweatshirt? or a long sleeve shirt? idk im not really sure. and if you tell me the top i should wear then plz tell me what material! (EX: a long sleeve shirt made of cotton, etc). oh also im a 16 year old girl and i want to look cute! and fyi the only sweats i have are black adidas with sky blue and white stripes on the side. so what should i wear! thanxzz :)