Measure North & South and then East to West. Should be 1/8" within each other.
Do this on your lid and top of the bowl (assuming this is for your OTG).
Also, is it new ? The newer lids seem to leak much more at first than the older ones did. mine gunked up and are fine on the kettles. On a WSM, call weber and have them replace it.
when i rehabed my neighbors kettle the bowl was really out of round. so i nade a tool to spread it and got it back into round, maybe a 1/16 off but at least the lid goes on.