① I thought I chased him/her down; however, I'm the one who was being chased.
② I thought I got him/her cornered, but actually I was cornered.
③ I thought I drove him/her into the corner, but actually I was the one who
「追い詰めたつもりが追い詰められてる」
① I thought I chased him/her down in the corner; however, I'm the one who was being chased.
※ chase down 追いかける、追い詰める
② I thought I got him/her cornered, but actually I was cornered.
※ get 人 cornered 人を追い詰める
③ I thought I drove him/her into the corner, but actually I was cornered.
※ drive 人 into the corner 人を追い詰める
I thought I was cornering someone, but I was the one being cornered.
"追い詰めたつもりが、追い詰められている"という表現は、英語で "I thought I was cornering someone, but I was the one being cornered."と言えます。
"I thought"は「私は思っていた」という意味で、"I was cornering someone"では「私は誰かを追い詰めていた」という意味を表現しています。"But"で文をつなぎ、「しかし」と意味の逆転を示します。最後の"I was the one being cornered"は「私が追い詰められていた一方だった」という意味です。
アメリカ合衆国 
