are you sure that the width and Height measurements are right?
that type of 55G tank is usually 48"L x 13"W x 20"H
I have a 75G that is 48"L x 18"W x 20"H, only difference is the width.
I had looked at the 55G but deciced I liked the wider tank more....
if you measurements are correct, than however sold/gave you that tank didnt know what they were talking about. hopefully you didnt get hosed by a LFS....
if you did, I'd try to get 20% of my money back......