Annoying they sold you a 5" wheel Michy! Petstores aren't always up on things and an assistant may not know anything apart from selling what's in stock. I would order the trixie or wodent wheel online and then take it back for a refund. Those two are probably the quickest to get hold of. The Trixie is easier to take apart and clean and the wodent wheel is probably the quieter of the two, but lots of people happily use Trixie wheels - some can be noisy, but not always - depends how important a quiet wheel is.
https://www.amazon.co.uk/Trixie-Exer...xie+20cm+wheel
Wodent Exercise Wheel - Junior on Sale | Free UK Delivery