what you'll need:
Cut out the cardboard. I made a big X, to say KISS
If you don't want to see the cardboard, paint it the same colour as the balloons, or your wall.
Punch holes in the cardboard, where you want to put the balloons.
The most practical is to start with the corners and the middle, then fill up the empty spaces.
Put the balloons into the holes.
Hang up the balloon message to your wall, use tape or if there is a screw in your wall use this.