Thickness is the wall, not a larger circle. The outer outline is still the radius you typed. Thickness 1 is that outline alone. Thickness 2 unions the next smaller outline. Thickness 3, which this page opens on, keeps the outer edge and adds two inner rings. The hole in the middle shrinks. It disappears when the thickness reaches the radius, because there is no inner outline left to omit. A filled plaza is a large thickness. A circular corridor is 1 or 2. A rim you can walk is often 2 or 3. People who wanted a bigger courtyard and raised the thickness have moved the inner edge, not the outer one. To grow the courtyard, raise the radius and leave the thickness alone.
Radius 8 and thickness 1 is 44 blocks. The same radius at thickness 3 is that outline plus two more, so the count on the result line is larger than 44 and the row table lists the thicker rows. Compare a row with what you have placed before you "correct" a gap. A gap on an inner ring is a missing block of that ring, not a reason to push the outer blocks outward. The outer blocks are the radius. They should already match the four axis ends.
The stair and slab letters are deliberately not on this page. They describe a one-block outline: a straight run as a slab, a turn as a stair facing away from the centre. On a wall three blocks deep those labels would be fiction. Every cell here is a full block in the count. If you later swap the top of a finished wall for slabs, treat the count as the number of positions, not the number of slab items. The stair page is the thin ring with the letters. The numbers page labels a thin ring by angle if you need a screenshot you can talk through.
Odd and even radii both keep the centre on a block. The centre cell is the origin. On a thin circle it is often empty, which is the room. On a thick circle it fills once the inner rings reach it. A sphere uses the same idea in three dimensions: thickness adds inner shells, and the layer slider shows one horizontal slice. That stack is on the sphere page. This page stays flat, one layer, so a floor plan does not get mixed up with a dome.
Build order for a thick ring: mark the centre, place the outer axis ends at the radius, then fill the outer row from the row count, then the inner rows. Do not start from the hole and work out, or the outer edge drifts. The PNG is the thickness currently on screen. A picture of thickness 3 will not match a wall you later change to 2. Download again after the change. Radius above about 30 is easier to place from the row counts than from the picture, because the picture stops being readable and the count does not.