We wheely hope you've been getting this one right - and we're already sorry for that terrible joke. Everybody who enjoys gardening probably has a wheelbarrow, and they're a standard tool of the trade for builders, too, so how come people can't say the word properly? It will definitely remain a bit of a mystery to us, if we're being honest.
It should be said exactly as it sounds, but we think it's the 'l' and 'w' sounds that get mixed up in the brain and cause problems. You've probably heard someone you know call it a "wheel-barrel". That would be a barrel for storing wheels, and to most people would be a completely useless tool, so put that away and make sure you ask for a "wheel-barrow" instead. You'll find it makes carrying things much easier.