Start with planning your days, how many free hours have you got in those 3weeks?how many units are there to be read?Which subjects are hard for you?which subject need more time and practice?Which class can you cut that wouldnt make a difference in your result(u can use that time to study more) ..so make your program based on those criterias.    Be honest and dedicated to it...it might be 1 units per day or so..so half a unit in the morning and half before sleep.     Time matters,so rearrange your schedule and get things done. Sincerely ThatDude