It is impossible to make terracotta blocks "point" in certain directions. As an example, when placing white glazed terracotta to create the "sunflower" pattern, there is no way to make the bottom left corner finish the pattern. Player angle & block selected don't grant this particular orientation. There are other orientations that are unachievable. Unknown if affects previously placed glazed terracotta blocks.

In other words, placing glazed terracotta to make patterns is annoying impossible.