I went from a hybrid to a road bike. It was true love from first ride (about 10 miles, next ride was about 50 miles), even though I knew I needed to mess with the bars a bit. Rode it a week, put in narrower bars and a taller/shorter reach quill stem, and instantly felt the fit solidify.
Haven't changed anything since.
If a bike frame doesn't fit you now, it won't fit you better later. Changing stems and bars and such should fine-tune the fit, not *make* the fit.
I'd still like to see you ride that Trek again, and really compare it to the Onix. You might find the Trek isn't as grand as you remember; or you might find that the Trek is lovely and you want it.
Either way, you will have a more complete experience of both bikes, and your buyer's remorse will be assuaged.
"If Americans want to live the American Dream, they should go to Denmark." - Richard Wilkinson