I guess what I'm getting at is that "comfort" is an entirely subjective concept, dependent not only on the person but also on the activity. Sitting on a cruiser bike might be considered comfortable but actually riding the damn thing any faster than 10km/h is definitely not, and trying to ride it up hills is completely impossible. On the Saturday just past the pros did the Clasica San Sebastian. I can assure you that they all used this agressive road riding position for the whole 234km (145.4 mile) course, becasue it is the most efficient and comfortable for the intended task.
However this leaves you in a bit of a quandry. You see, if you want an upright position with the seat and bars at nearly the same height, I would have recommended you a hybrid or flat bar or touring style bike, since those bikes already have a higher front end to satisfy your position requirement without a great deal of tinkering. Being stuck with the bike you have, there is really little you can do except play with the stem.
Unfortunately neither I, nor anyone else on this forum, can see what you look like or how you sit on the bike, so we arent't going to be much help to you in fitting your bike. It may well be that the stem you have is simply too long (making you feel stretched) and that you might be better off simply changing to a shorter one (they're usually available in 10mm increments) without having to raise the bars. Stems can also be flipped over giving an inch or two change in bar height, also without having to buy an adjustable stem. It may also be that you are sitting too high or too far back.
You may also just need to get used to the bike. Training is the best thing you can do and the sooner you start that, the more enjoyable will be the charity ride.
I'm sorry I can't be of more help, but there is a lot here that you will need to figure out for yourself. You might have better luck talking face to face at a shop or with more experienced riders. This, combined with your own experimentation is probably the best way forward.