I think the RR pipes spacing may be an optical illusion from the photo. How does it look in person? If it looks right there, then don't worry.
You measured 3 times, and I did a rough measure of the blown up picture on my screen and I think you measured right. You did right by placing the front RR pipe a ways back. At first I thought it was too far back, but I looked in RCA and Gunsmiths of Grenville, and the old ones had them a fair ways back ( 3.5 - 5.0 inches, says Peter Alexander). Another reason it may look a bit odd, is the distance that you have cut the forestock back for the muzzle cap, see my next point.
Probably too late now, but I think that if you make a normal sized nose cap, you will have an awful lot of barrel sticking out the front of it. I don't know the Winchester style, do they have enormously long nose caps? If you make the muzzle cap go almost to the muzzle, looks like it will be way way long.
I agree that the lock mortise is a bit fat, especially at the tail and the top. Hard to tell from the photo about the rest. Pictures of the lock mortise would help. I initially thought it was fat at front, but then thought maybe otherwise, hard to tell.
I think it may be the angle of the photo, but how much of the side flats of the barrel are exposed above the fore stock? Should be about half, maybe even a smidge more. Looks like less, but I can see that the angle of the photo is from slightly below, which makes it look like less is exposed.
Congrats on nearly finishing your first rifle, that is a big accomplishment. I know, I'm not that many rifles ahead of you at all.
My points are entirely about architecture, which is important, but I don't intend to diminish the fact that you built a rifle that will function, and most people won't notice these points.
Post more detailed photos, I'm sure we would all love to see them and help if needed,
Cheers
Norm