Hi Dan
Everyone has gone through doubts when learning to fly. But you've already shown that you can do it - by being sent solo. That's a big step, and somebody with good judgement has decided that you're very much good enough to cut it. Most people are pleased to get out of the circuit and do some nav, but also it is a bit of a come-down to be back dual again after the thrill of that solo flying. What I did for my students was to send them on longer and longer solo nav ex to build up their confidence for the bigger qualifying flights.
Don't worry too much about the planning. Yes, it is a big job to plan the whole nav ex out, with solving the triangles of velocity etc, but after a time it gets a whole lot easier. In any case, already you'll have found it is all a bit hit and miss, as you'll never know what the actual wind is, so before long, you'll become comfortable using guestimates. But of course, you need to do it all properly, fully, for the training and the test, in order to know the proper way to do things.
In some ways, you've answered you own question; if you don't enjoy planning and flying cross country, keeping within sight of the local airfield will quickly become boring. But I'm not sure you've given it a fair chance yet. As for the stress aspect, although rather time consuming at first, when it all seems very new and complicated, it should soon become easier and less stressful. In any case, if, as you say, you have a stressful job, isn't immersing yourself completely into a demanding but totally different environment rather therapeutic, especially when the responsibilities and the rewards are so high?
Good luck, whichever way you go.