Visitor Visa - B2

Hello!!

Sharing my experience... My application for B2 Visa got rejected.
Seeking an advice so I could get the pink paper the next time i apply:)

Im Single. 24 yrs old and i have relatives in the US. I applied together with my cousin, we did not apply as a family so we had a different counter.

My interview goes like this:

Me: Good Morning!

VO: Hi! Can i have your passport.
(handed my passport to him)

VO: whats the purpose of your travel?

Me: I would love to visit New York and spend sometime with my Grandparents.

VO: Are your Grandparents American Citizens?

Me: Yes. They are US Citizens

VO; How do they acquired their citizenship??

Me: Became nervous for a moment...
       I am not so sure how they acquired it ( and honestly I really dont have an idea)

VO: What is your work?

Me: Im a HR Assistant in a Testing Laboratory.

VO: How long have you been working there?

Me: more than 3 years

VO: Have you traveled before?

Me: Yes, I went to Italy, just last year.

VO: Are you married?

Me: No. Im single

After some typing... He gave me a white paper (214b)

During the interview proper he is just looking at the Computer and typing without even looking at me -__-

VO: i cannot give you a visa for now because you do not have a clear purpose.

Me: Thank You.

WAAAAAAAAAAAAA .... the feeling of rejection was just sooooooo T_T

Planning to apply 2 to 3 months from now..

He did not ask for any documents.
I was thinking that this question regarding how my grandparents acquired their US Visa triggered my rejection plus me being single and young. My cousin with the same age as mine got rejected too.. She had a lot of travels before this application (India, Netherlands, Malaysia, Georgia)

Please advice.

Thanks in Advance:)