Body Image

In 21 months I've lost 52 lbs. I am now a medium top. Tonight I was in the clearance section and saw this really cute dress that was a medium. My immediate thought is...that is small there is no way I can fit in that. I scooped it up and off to the dressing room anyway. It fit! When I look in the mirror I don't see it. I still see the fat me. How long with this take, because it has been months. I look at the dress and think....that is for a skinny girl, when I see it on me I see fat girl I use to be. As a reference I am 5'5" 167lbs. I was 220 when I started. My goal is 155. I want to know how to get over this. I feel it will be vital to maintenance.