What to do?

I am working on a hat. I got the pattern from DIY.com
it’s called edith’s hat on circulars. I have made 2 other ones in the past. The one I am working on now feels small.
Should I rip it and try bigger needles?
I am working with 9’s I have a pair if 10.5
I think the yarn is a little smaller than what I used before.
I just counted my stitches …I did cast on the correct amount
will it stretch when I get more of it done?
I have about 4 inches done.

You can put a piece of yarn through the stitches and try it on and see how it fits.

I’d be concerned that the 10.5 needles will make the fabric too loose and open, though it might be worth a swatch.

It’s because you used thinner yarn. Add about 4-8 more stitches to the CO to make it larger, and use the 9s.

I would start afresh… I have just done a lovely hat for my DD and used the wrong yarn AND needles can you believe that and it ended up fitting my 2 year old GS.