Entering without using Immigrant Visa

[ital$t1]

Hello everyone, I'm posting this thread because I couldn't find an answer to my particular situation, I hope somebody will be able to help me out. I recently went to the consulate in Naples to do the final interview and my immigrant visa was finally approved. They told me I have six months to relocate and after that, as soon as I pay the immigrant fees, I should receive the physical green card at my address in the US. This is the situation I'm facing at the moment: I have an upcoming trip to South America (departing next month) that I planned way before I even had the appointment scheduled at the consulate and I have a layover in Miami both going and coming back; can I enter Miami with a regular ESTA and then exit right away to continue my trip even thou I have an immigrant Visa on my passport? My plan is to move to the US after my vacation in South America because I have a lot of things to settle in Italy (job, house etc.) but I?m not sure if I will encounter some problems going through immigration.