hi , when you click the UV layout button maya will fit the uv's into the 1 to 1 space as best it can so it will scale them down but it should not stretch them.I myself and most users I think prefer to scale the uv's myself and move them to the top right square as i can arrange them exactly how i want for texturing.
scaling the u's down will make the texture bigger on your object which is why the squares on your body are bigger, you will have to scale the other part too to match.Try to keep all the squares as evenly sized as possible, it's not law but it will make matching your textures a lot easier.
unless you are extremely lucky some stretching after mapping is inevitable so you have to go into the UV texture editor and move each uv individually until you mininize the stretching, if you can't remove all the tretching then the thing to do is try and hide it in places it might not be noticable.