He is a High School Girl - That's one possibility off the top of my head
One of these? Sorry if they aren't the one you're looking for.
http://www.mangago.zone/read-manga/houkago_edge/
http://www.mangago.zone/read-manga/trap_in_a_skirt/
http://www.mangago.zone/read-manga/nijiiro_no_kimi_ga_suki/
Also, try this list to help you find it possibly:
http://www.mangago.zone/tag/crossdressing/?page=1
thank you for answering, but theres none of what im looking for :(
i forgot to add, its webtoon/manhwa cause its colorful
so what i remember is this boy wearing girl uniform and pretend to be a girl, its about school story.