It does indeed look like a very good instrument, with clean joints, and in very good condition.
Judging by the picture, and specifically the position and length of the Fujaku, your Shamisen is the correct length for a Nagauta, and should be about 99cm long.
I don’t see your koma (bridge) in the photo. You can try tweaking the position of the Koma, and try a different koma (maybe your teacher can lend you one).
If you have a plastic koma, the sound might not be the best, as a bamboo or bone would do.
Also, if your koma is new, it may not yet have the grooves to slot the strings. Please check that with your teacher, and ask her if she can do it for you.
If she can’t, then I can give you instructions for you to do so. It’s very easy.
As for your strings and neo, your strings are tied to the neo too close to the tip of the loop. The string should sit almost at the corner of the edge. Check the attached picture.