勘違い

I thought ...

～だと勘違いしていた

I thought they were open 24/7.

I was under the impression that ...

思い込む・てっきり～だと思っていた   impression（印象）

I was under the wrong impression that there is no class.

misunderstand

誤解する

That was my misunderstanding.

I mixed up the ....

日程や時間を勘違いする

I mixed up the time/date.