Have you got a picture? You can always contact axkid directly also x
One2 does have quite a narrow headrest. You can take the insert out sooner if it gives a better fit. My son has the insert out in this seat and he isn’t 105cm. Your retailer should still be able to help if you send them photos too.
Thanks all, as Emily suggested, I took the insert off and he looks more comfy, although I will email the retailer & Axkid also x
You should go back to the retailer. The after care is part of the price you paid, so it doesn't matter that is was a few months ago. Is his bum to the back of the seat when you put him in? Is the headrest the correct height?