[grbl Issue#1257] Problem with Y axis during arcs engraving

Hello !
I recently finished building my first engraving machine, it works well, especially when engraving rectangular shapes.
But when I try to engrave a circle or a round letter, such as a “O” I get this:
!rimg0786

The problem comes the Y axis which is too slow to start moving in the opposite direction.
And while the Y axis is static, the X axis continues to move so I obtain straights lines (as shown inside the red circles) and edges (as shown by the arrows).

Is there a way I can fix this ?
I did my best to explain my problem but there might be some english errors since it’s not my native language.
Thanks you for reading.