My passport stamp is for a month but my I-94 is admit until Sept 19, 2019. So that means I can stay in US for a month or 6 months as per I-94
A US visa allows you to show up at the border and ask for entry. You can do that at any time that the visa is valid.
At the border you'll be granted entry by the border guard for a period, which may extend beyond the validity of your visa. This is OK.
In your situation you can remain in the US legally for up to six months. However, if your visa application asked for a month and you then stay for six, there could be questions asked when you next apply for a visa about how you supported yourself during that extra time.
You can stay for six months, but in the interests of building a good travel history you should stick fairly close to your original travel plans.