Size deflation: like grade inflation, only backwards
Off-the-rack sizes became "smaller" as American women became bigger. Nobody wants to go to the store and ask where the size 94 pants are. So what was once a 20 became a 16, by decree.
Simplicity, on the other hand, being a pattern company, seems to have kept to their sizes over the decades, which only makes sense. Some of those patterns have been in women's sewing boxes for decades. It wouldn't be fair to the customers to suddenly change the designation of their sizes based on the embarrassment of people who're buying off the rack anyway.
You are still the same size you are wherever you get your clothes. Your measurements are just fine, and that's what counts.
I hope you enjoy your new sewing machine.