First check whether you have the correct screws for the job!
When assembling the Jamie Oliver wheels on your BBQ, you will see that there are four holes which correspond with four other holes on the bottom of the BBQ to align perfectly. But there is one step a lot of people tend to forget which makes it look like the first two screws fit, but prevent the remaining two holes from aligning which causes the screws to go in crooked.
There is an easy way to prevent this: Always work crosswise!
In the following image you see the correct order to assemble your screws, this will make sure all four holes stay aligned.