Hello Pawel, look at this sticker:
https://library.ldraw.org/tracker/25082
-has rounded edges (r=1)
-bottom (first block) at y=0 and color 16
-sides (second block), heigth from y=0 to -0.25, also color 16
-no edge lines
-uses prims
-printed top at -0.25
-origin centered
this is just an example, maybe copy the first two blocks and fit it to your sticker.
https://library.ldraw.org/tracker/25082
-has rounded edges (r=1)
-bottom (first block) at y=0 and color 16
-sides (second block), heigth from y=0 to -0.25, also color 16
-no edge lines
-uses prims
-printed top at -0.25
-origin centered
this is just an example, maybe copy the first two blocks and fit it to your sticker.