Well done on your first tour!
I never train - but sometimes I do practise. Load up the panniers and go off for a day, have a picnic, test out the stove, try out whatever needs to be tried out.
It's easy for me to say, but distance is not that important - enjoyment comes first. I think you're on the right track - trying to find places that are a shorter distance away.
Perhaps you could use your school contacts? Also, check out Warmshowers - it's like couch-surfing for cyclists. If nothing else, local members might be a useful source of places to camp or people to ask.
As for navigation, in my part of the world Google Maps is not for cycling! It's handy as a get out of jail option and for planning to get an idea of general distances and landscape. One handy feature of GM is that you can download a map before you go and use it to get your bearings. Even handier if you've marked off useful locations.
Cue sheets have their flaws as you have discovered, but really need to be backed up by maps, paper or digital.
A very handy app to have, if you have a smartphone or tablet, is Osmand. A bit of a bugger to learn, but free (at least the first sets of maps are) but very handy for seeing where you are. It will even plot routes totally offline. These might not be the best routes, but they will get you out of a hole. It's not as social media friendly as some apps out there, but it works.
Looking forward to hearing about your second tour!