From personal experience, I'd stay the course.
It could just be that your workouts produce muscle pump, as your muscles are swollen and trying to repair themselves... which may be the cause of your increased size.
However, this has nothing to do with why I'd continue on. I know from personal experience that higher rep work, which is in stage 1 getting you ready for the rest of the program, will minorly increase my size. However, switching to lower rep schemes (which are coming up) significantly decreases my size.
Now, the real question is, without knowing how much you're eating, do you know if you're eating too much? I'll say I highly doubt you're really all that bulky, unless you're taking those steroid shots in the butt you're not gonna go all bulky. However, minor fluctuations will happen... in weight, in size measurements, etc. Hell, you height varies throughout the day even... your body is constantly moving and changing and adapting... and right now with your exercise being every other day or so, you're not really losing that pump from the workout.
Think about the insignificance of that .4 pound measurement. That's less than a half a pound. If you just ate, your meal in your belly weighs more than a half a pound. (I know you're not worried about the weight, I'm making a different point.) Now extrapolate that to your other measurements. How much have they increased? which ones? Muscles that you didn't use before will prolly go up because you've increased their resting tone... shouldn't be much, and for most women the accompanying fat loss means that overall their measurements don't go up. For you, since you're so lean, it may be a bit different. But still, the measurements are so variable that they're not significant unless they're actually statistically significant.
But, here's the nice catch... gains taper off the longer you're at it. In the beginning, you're forcing so much new stuff onto your body, it can't help but change greatly to adapt. Your strength grows quickly because first it's just neurological, and then because your muscles have never been so taxed and scurry to catch up. But as time goes on, your body is used to the work and change happens more slowly. You can't always be "most improved."
Analogy: D student v. B student:
D student, with a 60% average only needs 10 points to get to a C, that 10 points is 1/6th or 17% percent of his starting average. So, his work of getting 10 more points results in a 17% gain.
B student, with a 80% average only needs 10 points to get to an A, that 10 points is 1/8th or 12.5% of his starting average. So, his work of getting 10 more points results in a 12% gain.
So, for those same 10 points of grade increase, the percentage of improvement for the D student is much higher than for the B student.
So, in the beginning of someone's training career, gains are great, percentage wise, but as time goes on it decreases. This is true whether we're talking about the amount of weight they're lifting (if you add 10 pounds to your 100-pound squat you're 10% stronger, if you add 10 pounds to your 300-pound squat you're only 3% stronger), the speed they're traveling, the growth in their bodies they're seeing, and sometimes usually the loss of fat they see as well.
So, even if you're gaining and your worst fears are true, and even if the changing rep scheme doesn't "fix" it for you, you're still not going to continue on a linear path of growth.
Not to mention... I highly doubt you're turning into SheHulk and bursting out of your pants. Not that it's fun to have to shop for a new wardrobe necessarily, but considering the benefits, it could be well worth the small detriment of being a smidge bigger... and if not it's quite easy to lose muscle... just sit on your butt for a while.
I'm personally betting it's mostly in your head with all those normal girl fears about eating and training and lifting heavy things and how to be "assertive without being a bitch" and "how to be nice without being a doormat" and other silly stuff society pours into us...