This is true for plotting or pantsing. Sometimes your muse or your characters have other ideas. That’s ok , let the words fall on the page before you fix them. I promise, every word you have to write will find the appropriate spot. Your first job is to find that spot, or something nearby.
The scene may go to unexpected places. The characters may try to derail your plan. Or you may end up far afield of what you plotted for the story. It will all work out. You may keep your surprises, kill your darlings, or make something entirely new. No matter what you do, the words will be waiting for your decision. You alone are in control.
Worst case scenario, you’ll rewrite a few hundred words. Count your self lucky that’s all you have to do. I’ve had to rewrite four introductions for what I thought was the first book in my series. I was mistaken. Those were four introductions for four separate books.
What you need to prepare for is your muse showing you a better path. Call it what you will, but when you see your book in a better structure, pay attention. Sometimes our best work is intuitive (or inspired). Don’t ignore those weird intuitions. They can be lifesavers.