Can I pair my Apple watch 8 to my Iphone that is only a 7

You can't. Apple Watch Series 8 comes with WatchOS 9. Any Apple Watch which is running WathcOS 9, requires an iPhone which can be updated to iOS 16 at a minimum. This means an Apple Watch Series 8 will not pair with such an old iPhone, such as iPhone 7. Either return the watch for refund or consider it's time to invest in a newer, more modern iPhone.

That's the move I would make. Enjoy the new phone and Apple Watch!