I have a J-1 to start mid June 2016. I entered the USA to travel 28 days before its start date and had to get an ESTA. At the border they wouldnt do anything with my j1 as I am visiting at the moment. How do I get the authorisation for my J-1 while I am in the USA?
The best way would be go out of the country for a short while (Canada, Mexico, most of the Caribbean islands), obligatory surrendering your I-94W (if you are given any) and reentering on J-1 in time. When entering U.S. you will have to specifically request being admitted as J-1. They will likely send you through a secondary inspection (if entering by land), talk to you, and issue you a paper I94w (if entering by land). Remember to keep it with you and surrender upon leaving the U.S.