Congratulations on finishing the game for game jam XD I'm glad you finished it so now, you can take a rest after a long time hardwork. XD
I think one of the way to do it is via Unity Tilemap.
https://learn.unity.com/tutorial/introduction-to-tilemaps#
https://docs.unity3d.com/Manual/class-Tilemap.html
That way the ground is placed on tile with same size, and aligned within grid.