I lost track of time.

我把时间搞糊涂了。

I didn't realize it was so late.

我没意识到已经这么晚了。

I overselpt.

我睡过头了。

My alarm didn't go off.

我的闹钟没响。

Traffic was slow.

路上有点堵车。

I was stuck in traffic.

我在路上堵车。

I forgot my computer at home, so I went back for it. That's why I'm late.

我把笔记本电脑遗忘在家里，所以我回去拿。因为这样我才迟到。

This is the first time I've ever been late. I swear it won't happen again.

这是我第一次迟到，我发誓再也不迟到了。