This one fairly tough but if you are still having trouble with it clear your system cache and reboot the game without accepting the update.
Instead of playing the game as you usually would, simply collect one crystal at a time. This will trigger a new wave of enemies. Be sure to kill them all before collecting the next one as there is a limit placed upon the number of baddies spawned per crystal.
Also, try to save your bombs for nearer to the end. They may very well make or break you. I believe I started using them fairly often at around 25 lives.
Follow these steps to clear your system cache:
Dashboard > My Xbox > System Settings > Memory > press Y on Hard Drive