英语翻译：我错把XX当做YY、

I have mistaken XX for YY.

mistake for: 把…错认为...
例句：mistake one thing for another.
把一种东西错当成了另一种
见http://www.iciba.com/mistake...%20for (ICHIBA 词典网页)

confuse sth with sth

I mistake XX as YY.
如果是已经发生的事，那mistake就要改成mistook。

错把冯京当马凉吗？mistaken identity

i have mistakenly identified XX for YY

or I have mistaken XX for YY

I mistake XX for YY