Cross country

so this year I decided to sign for cross country for school (it’s high school cross country) and we just started practicing yesterday and all the other people on my team can run the full 2 miles but I’m always stopping or taking the shorter way. Now this my first year doing this but I have played sports before and am very active but idk I just can’t keep up and have to walk bc my legs hurt so bad. If any of y’all have done cross country or track or are active runners, can u please tell me how to increase my stamina?