Anne, your inkwork is very nice. I am referring to the quality of your lines and the variations in your marks. You are absolutely correct about the error in perspective. There are also two other small errors: 1. from what appears to be your eye level, the top of the parapet would not be visible; you would only see the edge of the parapet, and 2. the height of the parapet in the sketch would be more on the right side of the sketch (since it is nearer to the viewer) than at the left side of the sketch.
I think all of this could be corrected (visually) if you decide to make the top row of bricks (or stones) darker, slightly adjusting the height in the process, and ensuring that the top of the parapet is not visible. I would suggest that you print a copy of your sketch and test out my suggestion before you do anything on the original sketch.
Your sketch is very attractive even as it is.