First time travel to the USA

I have a B1/B2 5years with multiple entry. when i was applying for the visa i stated i will be staying for 2 week, my question is can i buy a 1 month ticket when travelling?

You can stay for a month without any issue. It doesn’t have to match what you said during the interview (example: 2 weeks; people generally give an estimate during the interview). You will be fine as long as it is less than 6 months.

Thanks for your responce it really help, and one more question at the POE can i use a master card to present if am ask about my pocket money?

During the interview, you might have taken financial documents (bank statements, etc.,) to support your travel. If you have it, take it with you. It might be helpful at the POE. Telling that credit card is available to support your expenses might be okay to tell at the POE.