Nells - I've got the Mio Link and the only thing I would say is that you need to wear it higher up your wrist than a watch, to ensure a close fit. If you wear it on the same wrist as your watch, you'll be fine.
Tricky - I did a similar thing when booking a non-refundable Eurostar trip a few years ago. I phoned them up, told them I'd been really dumb and I-know-it's-non-refundable but pleeeeeaaaase, just this once. And they did.