First off, make sure you are running 3.30 OE. To check this go to System Settings->System Information. If your PSP says 3.30 and not 3.30 OE-A then you screwed up. If you are indeed running 3.30 OE-A, then here's how to access the Recovery Menu. When turning on your PSP, hold down the R button. You should then be able to downgrade back to 1.50 if you follow the guide.