Do I have a bad head gasket?

"with on water in it"? I assume you meant "with only water", and not "with out water"? If so, and JMO, you're lucky if it is just a head gasket. Leave the cap off and fire up the engine, look in the rad- if it's pushing a steady stream of bubbles, you've got a compression leak somewhere. Run a compression test to localize the issue. Could be multiple points. Depending what the compression test tells you and where, that's the head you pull and inspect... could be gasket, cracked head or cylinder...
And now you know why you don't store it without antifreeze or draining it... :(