I'm following a blender tutorial and it was explained how to mirror my object. I put the origin in the center and then applied the mirror modifier, but rather than the leg mirroring across to the position of the opposite leg, it mirrored right next to the original leg, like so (ignore my amateur sculpting):

Could anyone explain what I might be doing wrong?
Thank you so much for reading!
EDIT: Thank you Mr Zak for your response. I am still having problems however, and I think it's something to do with how my object is placed in relation to my reference image.
When I'm zoomed far out like shown below, the leg appears like it's in the wrong place, misaligned to the right.
Zoomed in to where it was on the first image I posted with the mirroring, it appears to align with my reference image.
Finally, When I zoom in more closely the leg is misaligned again, this time misaligned to the right (I would post a picture of this, but I have not been a member long enough to have the permissions to post another link).
I feel like I must be going about things the wrong way in terms of camera angles. I am constantly having to readjust my camera to align properly with the reference image. To get to a front angle, I generally click View>Right and that orients me looking at the image, but it's never at a consistent distance/panning, if that makes sense, and I have to readjust so that my object is lined up with my reference. I feel like the guy working in the tutorial I'm watching does not have to readjust the way I do, so I feel like I must be making errors there.