When communicating in Chinese you may often make mistakes using Chinese grammar like:

False:

    今天是3月20天。

    Jīntiān shì 3 yuè 20 tiān

True:

    今天是3月20号。

    Jīntiān shì 3 yuè 20 hào.

 

“天”和“号”混淆，应改为“3月20号”，口语里常用。书面语里还可以用“日”。

The speaker has confused the word 天 with 号 which is the proper word to be used here. An alternative to 号 is 日. But 号 is frequent in spoken Chinese whereas 日 is often seen in written Chinese.