You need to beat level 4-3 without losing an orb.
The best way to make this easier is to first reach level 4-3 and immediately save your game from the pause menu by selecting save & quit. Then resume your game and try to complete level 4-3 without losing an orb. If you lose an orb, immediately quit the game by jumping back to your desktop with the Windows key and close the game.
Re-open the game and resume your game and you'll be back at the start of level 4-3 where you can try again. Repeat as necessary until you can complete the level without losing an orb.