Displaying Icons using GridLayout - Java

[BlueChinchillaEatingDorito]

So I'm making a maze type of game for a school assignment, and I just can't get the maze portion to display correctly. Right now, I have this. I'm using a GridLayout of (20x15) but all it's displaying when I run it are only two icons organized vertically, any ideas?

    private void updateGamePanel() {
        for (int i = 0; i < 15; i++) {
            for (int j = 0; j < 20; j++) {
                if (!instance.isHidden(i,j)){
                    if (instance.isMazeWall(i,j)) {
                        add(wallImage);
                    }
                    else {
                        add(hiddenImage);
                    }
                }
                else {
                    add(hiddenImage);
                }
            }
        }
    }

wallImage and hiddenImage are both JLabels of icons.