I am going in less then a month to the United States for a 3 month period. 
I already have an ESTA that's valid until the end of the year.

I already have my flight tickets, but I read somewhere that I am allowed to stay 90 days, but unfortunately I counted the days I am staying are 91. 

Do you think I will have problems? My ticket its not refundable, so I really didn't want to pay for the excessive fees they charge for changing the dates.