this game?
if yes,i know a little trick to level up fast.
1.play on any mode, try to get the high score, so u get a lot of XP.
2.after you finished step 1, play again on the same mode, click start. when the enemy appear,click menu, click quit. you will got xp,same amount with XP on step 1.
3. repeat step 2.
hope this help. sorry for my english :P