First time is always the hardest. The next thing you build and carpet will turn out better. Then the next, better yet. I also vote for "good job" on your first carpeting attempt.
As a side note, to keep from seeing the screws, just be sure to assemble the piece as much as you can, i.e. in a sub enclosure, everything but the sub and terminals or binding posts. That way, you can hide 99.9% of mechanical fasteners with the carpet. The two biggest reasons a lot of us carpet are 1. Hide the screws and 2. Hide the bare wood.
All in all, great job. Keep it up!