What size wood are you using?
I made mine with two 3"x4" pieces of wood, they are 18 inches long and sit back to back so the top surface is 8 inches deep. Then 2 bits of 2"x4" are nail to the bottom for feet which holds them together.
I rounded the edge off with a plane and some sandpaper.
It will always be difficult to balance with a barbell as you cant hold on to anything.
If you can get close enough to a flat wall, hold the bar in a front squat position and let the plates roll up and down the wall so you are leaning very slighty into it for balance.