the GMAT already partially offsets the GPA. there's not too much else you can do except take community college courses. given that you already majored in industrial engineering (and minored in economics, so i'm guessing you at least took the intro level business courses) then there's not too much value in that.
one tip would be to get involved in an extracurricular. it doesn't have to be a save the world type thing - it can be anything from a professional organization to a local volunteer group at a church or school. whatever it is, make sure you enjoy it and are willing to stick to it.
another that goes without saying is to do a good job at work. you seem to already have the right idea, since you were commended during your internship. this is important because when it comes time to get letters of recommendation, people will write based on how good of a team member you were.