Where do I store my gas for the lawnmower when it's 105F?

I have a small (one gallon) approved red gas can that I keep lawnmower gas in. As the temperature has been rising the can is swelling. My garage is not cooled and I don't want to store it in the house. Is the swelling normal? Is it dangerous? Oh, it is sealed with a spout and I have to either pull the button to pour or let it go to store.
I looked for a vent on it and couldn't find one. It has one of those toothed caps and I turned it until I heard it hissing. Hopefully that won't cause any problems but it feels safer than a bulging gas can.

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