...there are rerolls available for the 2nd and 3rd tiers (of normal levels), lol. Just reroll until Glass becomes an option. It only costs like 200 Rep (the heart currency).
Viewing post in SpunkStock: Music Festival v0.12 Demo comments
Wait, your problem was simply trying to BEAT the levels? This game is lenient enough I didn't imagine that could be the issue (and more relevantly, I somehow managed to completely miss reading that in your comment, my bad), but yeah, when it comes to that, you really do just need to be fast enough and maybe roll a few decent (or just effectively null) perks.