Upvote:1
First rule: you need to convince him/her that you’re going for a visit and you’re not desperate(you won’t overstay your visa). Major mistake I see people making is they act like it’s an interview for something which is out of their reach. It really isn’t.
It seems your first mistake was being proactive about your documents - why do you want to prove something you’re not asked? Don’t give him/her your documents unless you’re asked.
Second thing, be casual in your behavior. You really need to make him/her believe that it really doesn’t matter whether you get visa or not. Your language should be as if your close colleague was asking you these questions. Also, make sure you show your salary/funds are enough that you can casually visit USA or get someone from US just to show them as your sponsor.
And lastly I’d say, wait for a year now or at least 6-8 months, apply next year for the same conference and don’t make same mistakes.
It still needs a little bit of luck. I hope you get it. Best of luck.
Be happy even if you don’t get it, it’s not end of the world, just a bit tricky system.