Jīntiān shì 3 yuè 20 tiān.
False: 今天是3月20天。
Jīntiān shì 3 yuè 20 hào.
True: 今天是3月20号。
“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 wheras 日 is often seen in written Chinese.
