This video gives you a good tip on how to measure for curtain rods. You want to go 2-4 inches past the window casing. You might not have thought about that and just gone ahead and only measured the actual window like you would for blinds. You actually want the curtains to go on the outside of the window. And if you have a wide window, you want to measure out even more than a narrow window.
When measuring for curtain rods, I like them to extend between two and six inches outside of the window casing. That’s this trim that surrounds the window. Go a little bit wider for wider windows and a little narrower for narrow windows.