blown base gasket?

[steven 250sx]

well I noticed there was gas leaking down my right side cover from my cylinder. yup blown base gasket, but i took it apart and the gasket was fine well it looks a little strecthed but not ripped. could it be my cylinder nuts got lose? also my piston says 2.00mm that would be my last bore correct?

p.s. first time i had my top end off.