Actually, for a first dress, it's got a lot of good stuff going for it!
I think the biggest "well, consider this other thing next time" elements would be to possibly switch back to rectangular panels rather than gored panels, so the formality of the skirt style matches the formality (or lack thereof) of the fabric and bodice.
The length on the bodice looks quite good. It's not too long, which is often a problem with first dresses. You could move the pleating closer to the center front, so that the outermost pleat is about where the innermost pleat is right now, and that will narrow the whole look in the waist a bit, and give a more period line to it. It'll let you keep the sides very smooth and fitted, and that's always pretty.
The center back fullness is handled well, but skewed away from your center spine, so that can be either fixed on this dress, or watched closely on the next.
You may find, when you move the front pleats toward center, that the whole side bodice is actually a few inches big! I'm thinking it is, because the shoulder drop is pretty large... it could be reduced a few inches, and still be very period, and narrowing the whole bodice from center bust toward the side would also eliminate most of the little fold of fabric just above the bust.
Now, for wearing this particular dress and using it for 1865? I wouldn't worry about that reformation at all. I'd just re-seat the front and back fullness to a better alignment, and any extra in the upper body can be written off as the working class re-using a previously-worn garment, or you have changed shape.
The skirts could use a few petticoats under to boost the shape; the length is fine for a young lady, in my opinion. If you find you need to rediscover some length, pull out the turned hem, and switch to a faced hem, and you can "find" another 3" of skirt length, it looks like.
If the neckline is pulling at all, take off the binding, skim off about 1/8" at the center front, and tapering to nothing at the shoulder, and re-bind.
I think you've got a great start--this is a dress you could easily use for any everyday lower working class look!