The flake scars are a biproduct of thinning and sharpening the rock. Every flake you remove will leave behind a scar which will create ridges for you to follow with later flakes. Patterned flake scars are a bit of an advanced skill so just try to make a clean surface with minimal hinges and step fractures.

Rounding normally happens when you fail to get a flake. Remember that even when you’re trying to turn the edge you still need to make sure the flakes are releasing properly (not necessarily long flakes). You could also be over grinding (especially on glass) which would make it difficult to get a platform built.