Accidently used wrong needle size

I am making a scarf (i have knit other things but I would say i am still a beginner) and the pattern calls for size 9 needles. I started the scarf using the size 9 needles but somewhere along the way i must have picked up the wrong needles and started using my size 7 needles (that look exactly the same). I didn’t even realize it until i decided to start another project and couldn’t find my 7 needles!
Should i start over? If i switch back to the size 9 needles will it be wider on one end of the scarf than on the other? And, the sides are really curling in a lot. Could this be due to my using the smaller needle size? Any help or suggestions would be greatly appreciated! thank you!

Yes, it’ll definitely be wider where you switched. The curling is normal if you’re doing stockinette stitch (knit a row, purl a row) regardless of the needle size. So you can fix 2 potiential problems by ripping it out. Start over with the size 9s for the right size, and knit a few rows in garter or seed st and continue them on about 4-5 edge sts to help keep it from curling.

depending on how far you have gotten you could be creative and randomly switch guage and have a scarf that gets wider and narrower

but best would probably be to frog to were you switched (if you can the switch)

one thing i like to do with my straight needles (bamboo/wood) is paint a band of colour on them (near the end - not the point) with nail polish… that way it is easy to grab 2 of the same

or with metal needles i buy different colours - my size 2 are red (both DpN and straights), my 7 are purple, 9 is gold, 10 and green, 13 are gray