I'm an American that has lived abroad twice and spent time in over 50 nations.
You really waited to the last minute on this. Most visas take 3-9 months. I would suggest your best option would be to try to apply for a student visa. I think it's called F-1
Likely you can get a B1/B2 visa. You should be able to establish a US company with B1/2 visa, however you can't work for it.
* personal opinion only, not a legal advise.
A couple of friends of mine came on a b1 and had no issues in NYC just make sure u bring all the papers and demo with u in case they ask.
Oh and by the way u don't even need a visa to open up a company in the states, u can do that even online, so no worries on that end
You are screwed. This is way way too little time to get your visa situation in order. Consult an immigration professional immediately to have any hope of success.