How do I make a hat smaller?

I recently used this pattern to make a hat, adding on some stiches because I used a smaller pair of needles. I seamed the hat to see if it fit, and it’s far too large. I picked out the seam, but how should I make it smaller without undoing the whole hat? I was thinking of seaming it where it would fit, and then cutting off the excess, but is this a good idea?

Thanks.

It might work if the seam is very secure.