N600 wifi extender running at 100mbps instead of 600mbps

I purchased a n600 wifi range extender from best buy. I installed the device making sure to put it in an area with already good wifi reach. When I used an ethernet cord to get internet from the range extender to my desktop pc it showed speeds of 100mbps instead of the advertised 600mbps. I would like to know if there is something I missed while installing the device which would remidy the problem.