Affinity Photo /designer lacks an ability to work with packed RGBA files .If alpha is zero Affinity opens it as a black hole in RGB channels. Also I miss pattern preview from Photoshop . You can construct the same in Designer using symbols. But it would be a mess of layers . Brushes and layer system are both more advanced…
select the outer border one edge at a time, align the verts until it's straight. then select and relax the inner verts or, use relax using ignore outer border.