① You’re thinking too much.
② Don't put too much thought into it.
③ It's all in your head!

举例
场景一
Emma:I think he likes me. Every time I see him, he’ll smile to me.
Emma:我感觉他喜欢我。每次看到他他都会冲着我笑。
You: It’s all in your head! He has a girl friend now.
You:你想多了。他已经有女朋友了。

场景二
Jackson:I think I am gonna win the lottery.
Jackson:我感觉我要中彩票了。
Tim: You’re thinking too much.
Tim:你想太多了。