“我不是故意那么做”的英文怎么说

I didn't mean to do it(that).
因为事情已经做完了，所以用一般过去时态。书面语，口语都可以这样说的。
或者更正式一点就是，I didn't do it deliberately.

I didn't do that on purpose!

“我不是故意那么做”
I didn't mean to do it.--------比较口语说法

I did not do it on purpose.----偏向书面表达

呵呵. . 又学到知识了

I didn't mean to do it.
I didn't mean to do it.

书面的话，可以说

I did not do that on purpose.

口语化的话，就是

I didn't mean to do that.

书面的: It was quite without intention
口语的: I didn't do that on purpose 或者 I wasn't 根据语境了