I've been thinking about this giving yourself challenges thing. You see, I was an over-confident low hours PPL, who thought I could fly anywhere. I think we're probably at least as common as the under-confident won't-leave-the-circuit types, and far more dangerous.
Perhaps the secret is to give yourself challenges, try new things, but ONE AT A TIME. So either fly to a new airfield OR go through a MATZ OR get a Class D clearance OR cross a large expanse of water OR travel from one end of the country to another. Once you've done some of those, you can add in others. The trouble is, if you haven't flown outside your own area or landed away in the UK, a cross channel trip requires rather too many new things. So, actually, does a trip from Norwich to Newcastle - lots of MATZes and controlled airspace en route; get used to talking to them first.
None of these things are difficult, ONCE YOU'VE DONE THEM. But if a new pilot does all of them for the first time, he/she is likely to be at the limit of what they can cope with. And then, if the workload increases at all due to weather or something unexpected, they hit overload, which can be dangerous. One option is taking a more experienced pilot along for the ride. Another is to take things slowly - which doesn't mean at snail's pace.
After all, what's the rush? France will be there next year. There is a balance between never leaving the circuit, and doing it all immediately. A PPL is a licence to learn, and nervousness is sometimes there for a reason.