[Umbrella Chronicles] Help with S-ranking Umbrella's End 3 (TALOS level)

I'm about to throw my Wii remote at the TV screen now... This is getting ridiculous.
Basically I chose the one path in the maze that has 5 steps instead of 6, and I did NOT get a game over once, not even right after the checkpoint; yet I still only get a B for time??? I got S for everything else, just that stupid B for time ruining everything!! GRRR. I really don't know how I can improve the speed to an A... I mean sometimes I would accidentally wipe out enemies with an MRL (because with a bunch of weapons it's hard not to confuse which weapon you're using), which could only IMPROVE the time, and I used like 6 MRL shots on the final boss, using barely two minutes in total on both forms of the boss. What am I doing wrong?? Any tips would be appreciated.