On the HRM strap thing - it was definitely too loose yesterday, granted. When I was using it last year I had it really really tight and it was still rubbing.
I think it's to do with the positioning / weighing down that occurs by the plastic monitor clipped onto the front. Because of that, the elastic strap is slightly pulled away from the chest and no matter how tightly adjusted, there seems to be a bit of "give" between strap and breast bone area.
I have an HRM that I started using last year until it rubbed so much on my chest on a 15 miler that I was bleeding by the end of it. It's been worn a handful of times since. In fact, I strapped it on yesterday for a 60 minute easy run just to see what the readings said. Right enough - a rubbed bit on my chest by the end of it, thankfully not bleeding this time though.
I don't really have any advice to offer I'm afraid, but just wanted to say - 3.5 hours on a cross trainer?? Jesus, that sounds dull...
Hope your injury worries clear up and best of luck. I am confident that if you've done the training properly up until now and keep the aerobic training up over the time you're not running, that you'll finish the marathon and not be a million miles away from your target.
Aiming for 6:55 - 7:00 per mile, so happy with that. My Garmin had died when I took it out of my bag so had to mess about with MapMyRun which wasn't as bad as I thought it would be but as I couldn't programme intervals in, I had to record individual workouts - bit of a faff, but not too bad.
Off the back of a pretty heavy week so far (just shy of 30 miles now since Monday), so really happy to have pulled this one in on pace. Easy running until Tuesday where I've got the BIG one - 8 x 1000m at sub 40 pace. Confidence is high now...