I would have listened to that voice in my head that said "oops, you've knit a bit further than you probably should have before joining the front", and I would have ripped it back a bit then.
I would have tried it on just a little bit earlier.
And most importantly.... I would have checked the pattern before ripping it out entirely, and then I would have known that the next size down actually requires casting on the same number of stitches as the size I originally started.....
Hindsight is a wonderful thing.