Yes and it always will be 128KB. If it is any other size then that file is no good. So forget about the fact that the file size did not change. The more important question is since you ran x360sam v0.4 you should have a new file called hacked.bin. If you do then just run the samhack batch file and it will flash your drive and life will be good.
Um, it should be 256k (262144bytes).
And foaley has already worked this one out.