So I got PSP Go and it came with Rock Bank Unplugged. 
 
I was playing it and I unlocked Montreal. But in order to unlock the next rock competition, it says I need to get two more stars within Montreal. The problem is that I can't get more stars unless I download some songs from PSN, which is really really weird. I got full stars from other songs but it still says I need to get two more stars but, like I said before, I cannot get two more stars unless I buy two songs from PSN. I know people didn't like Rock Band Unplugged but I am pretty sure it wouldn't "force" you to buy songs.
 
Do I actually need to buy songs to unlock more stuff? or am I doing something wrong? 
 
Please help me!