I did make a muslin to see how big it would be, and it is huge enough to fit everything a nappy bag needs without enlarging it all (in fact it's so huge it hides my basketball belly!). The only modifications I made was to add some pockets to the inside lining in a contrast fabric, and to add a magnetic snap closure because the pattern didn't have any closure to it at all. I used black corduroy for the straps, which by complete fluke was a brilliant choice because corduroy is a grabby fabric and the straps don't slip down at all. I left off the contrast panel at the top of the bag only because I wanted to maximise the amount of the main body fabric that was visible.
And thanks for all the birthday wishes to my last post, especially from my sewing fairy godmothers LOL! First week of pre-baby holiday has been absolutely fantastic - sleeping in, shopping, leisurely breakfast and lunches, of course all this will end when the baby actually arrives but I'm sure I'll be too happy to care about that (fingers crossed!)