If you're still within the 14 day return period, take the iPhone 7 Plus (if that's what you have) back to where you purchased it and exchange it for an iPhone 7. Should you have gotten the iPhone 7? Probably.
I wanted to go back to the 4.7 size, the plus does not fit well in suit pants, dinner tables, long conversations...Should I have gotten the 7? I like having a headphone jack. I use it in zoomed view, coming from a Plus it's nice.
For me, the 4.7" size is the sweet spot. While i don't mind the 5.5" inch screen size, the bezels are just to big and makes the phone big. If i purchased an iPhone today, i would most likely go for the 7. But that being said, if you really want the headphone jack then the iPhone 6s is for you. It also means, you won't have to spend extra on dongles / adapters to get your wired headphones to work. Which is a nice plus. It's still a fantastic device so don't think of it as 'old' because it really isn't. And the performance is really great.