我错认为那是一次非正式的会面。

I was wrong about it being a casual meeting.

《柯林斯英汉双解大词典》

“聚会”指的是一个非正式的会面。

A "get-together" refers to an informal meeting.

youdao

为了保证安全，她建议：“一定要计划好正式的会面结束之后去哪里。”

And, just to be safe, she advises, "Always have a plan of somewhere that you're planning to go afterwards."

youdao