I studied for all my subjects not even leaving out one of them.
I studied for all my subjects not even forgetting to study for one of them.
I studied for all my subjects は全教科勉強したと言う意味です。
not even leaving out one of them は一つも残さずと言う意味です。
not even forgetting to study for one of them は一つも忘れずにと言う意味です。
お役に立ちましたか？^_^
アメリカ合衆国 
モロッコ 
