Hi,
Firstly, I like the style! It feels clean and minimalist, like it belongs in a courtyard surrounded by greek columns or something.
Just a few things, which are shown in the picture below:
-
ndchristie is right, the perspective is a bit off. Aside from the 2:1 ratio that has been described, you can judge whether something is the right proportion by measuring the distance from the corners of the floor to the sides of the fountain. These distances should all be equal, and you have a convenient pattern of tiles which shows this nicely. I have added some rulers to show it.
- The fountain itself is an odd number of pixels wide, this means that it can't be properly centred on a canvas that is an even number of pixels wide. This is most obvious when you look at the centreline, which I have highlighted in white, but you will have to zoom to clearly see what I mean.
- The centres of the circles are not all on one axis. The circles on one plane (e.g. the floor, shown in red) should have the same centre.
- (very minor) There are a few stray pixels hanging around on the outside, shown with arrows.
If you construct your outlines starting with the floor, then moving upwards, it is much easier.