Keep my bike?

[Owlie]

You sound like me---you don't take--not failure, exactly--but not living up to your own initial expectations well, do you?

It sounds like you want permission to give up on the Hardrock and go for a road bike. Don't give up on your dreams of riding on back roads just yet. Treat it sort of like interval training. You can only do x miles? Okay, then ride x miles on a regular basis until it becomes easy. Then move on to x+1 miles.

Riding your Sirrus should help with overall fitness too. But I agree with Blueberry--give yourself some time before buying another bike. Do some research, and maybe you'll want to keep the Sirrus for just tootling around. Nothing wrong with that.