Get/have cold feet （做某事前，因为紧张或害怕）临阵退缩

If you get cold feet or have cold feet about something you have planned to do, you become nervous about it and not sure that you want to do it.

She had been looking forward to the bungee jumping, but she got cold feet right before the jump. 她一直盼望着去蹦极，但在跳之前却退缩了。

Tomorrow is your big day. You are not having cold feet, are you? 明天就是你大喜的日子了，你不会是想临阵退缩吧？