How can i get motivated to do the things i want to this summer?

im a high school student and im too young to have a job so i had these huge plans for this summer. Well ive already been out of school for 3 weeks and havent done any of that:/ Im supposed to run 100 miles this summer for cross country but i cant get motivated enough! ive ran 2 and a half lol me and my cousin and a friend of mine were all gonna run together all summer but that hasnt happened yet. I was gonna work out and stay fit. i mean im super skinny still and never physically get out of shape but i havent continued to run from track season so im probably out of shape running-wise now. I was going to learn how to skateboard this summer but that just doesnt sound fun. I also was going to paint and draw when i got bored but that has only happened once or twice. And the last thing i was gonna do is get a job around my neighborhood but idk what i could do thatpeople would actually need help with..i mow lawn for my gramma but thats it. HELP! i need a way to fix all of this! and please dont be rude! i know i gotta get off my lazy and do all of this but i just feel like its too much to do!!