Hey, no worries there! I just finished printing parts 1 & 2 today and they are not matching up very well. I have a feeling that Meshmix altered the scale of the original part, but I also noticed that parts 1 & 2 print on different seams. To test the theory that Meshmix screwed up the scale, I loaded parts 1 and 2 in MatterControl and yes, they are slightly different. I would think parts 1 & 2 would have exactly the same measurements but they do not. Must be the way they were sliced from the full helmet model.
I've been using Hatchbox ABS with a 0.4mm nozzle, printing at 235 degrees. I've had some layer separation issues and tried to kicking the heated bed up to 100 for Part 3 and that seemed to do the trick. I also shut fans down to 20% as well.