there is another block - besides the plus shaped one - with which you can use the size trick to get on the walls
I was looking for a route almost identical to yours, but I ended up finding a much much shorter one. If you push one of the message notes up to the breakable wall just above the hive are and drop the stone on there while it's in between blocks, you can clip very close to the star
Do note that on the right at the bush area there's a big open area, This is needed, because after you get up there the first time, you won't have the room to become small again in the main area, so you'll have to clear out that section on the right to become small again after setting up the rock at the top