You are perfectly fine with your items and attributes, you should face no troubles. I really don't get it why you can't finish it, because I did finish it with no problems. The main thing I was doing is bursting enemies with Shatter + Icegrenade and I always killed big guys first. I also stood at the end of the area so that I could confront them immediately and they would have to travel longer distance. Last minute was immense, yet I just had to hold enemies for that time without killing and after timer expired they all died.
