Some budgies are bigger in size and do get an heavier build when compared to others, your Berry does appear to be a bit chubby, but as long as he is active, is able to fly well and you keep on giving him plenty of exercise and a balanced diet, he should be well.
In my flock I would rather have my birds not too thin because when fighting an illness they go downhill faster when they do not have any reserves in their bodies. The first thing to go away when they are sick is their appetite in most cases, and the bit of fat they have left in their bodies can help them when they get sick.
RIP sweet Tito (Summer 2008 - January 17th 2013).
You are missed and never will be forgotten.