I made a mistake with the presentation.

我在做演说时犯了一错误。

Just relax. Don't take it too much to heart.

放轻松。不要太放在心上。

Just relax. It's just because the paper is too difficutt.

放轻松。那完全是因为试卷太难了。

But there are still passers among us. Maybe I didn't work hard enough.

但我们中间也有人通过。也许是因为我还不够努力吧。

重点讲解:

Calm down.

Just relax.

calm down通常是用在当对方比较激动或混乱时，让其冷静一下，思考一下对策或者别干傻事。如果只是单纯地放松，老外经常挂在嘴边的则是：Just relax.简单明了，张口即来。