How can I get like a good jaw line? orr whatever..keep reading?

wait let me rephrase that......im not fat or anything but i want a good strong visible jaw line..but my face is all round and cutsey....and thats annoyying because i have to leave my hair open all the time otherwise if i tie it..then my head looks too small for the rest of my body....weird....so how can I make it bigger...or atleast less cutsey..if not bigger..beuase i really want a good strong visible jaw line...and not im just round