Ahh…yes…changing the needle size would have exaggerated the problem. The knitting at the top near your circs/needles is not showing the same problem in the main as compared to the bottom is it. I think what you’re seeing now…near the needles, is the right tension basically but with a slightly finer yarn than intended (you agree with that earlier in response to MerigoldinWA).
Blocking will resolve a lot of the issues however if you’re really unhappy with the bottom of this piece I think you need to undo and start over and just stick with the needles you’re now using. Doing this won’t be a problem for the yarn (referring to my previous post).
In the future perhaps swatch and use that to experiment with needles rather than doing so much work on your main item? A learning curve