I didn't start running until XC season during my Soph year in HS. I incorporated Sunday long runs beginning in the Summer between Jr and Sr years. I continued Sunday runs throughout my Sr year.
My mile time went from (Soph > Jr > Sr): 4:55 > 4:35 > 4:15 and walked on a P5 D1 program. The Sunday long run was the number 1 reason I progressed.
So, keep it up!