First thing I noticed was that you grabbed ZERO times during that game. Sometimes you could have a shieldgrab but you instead opted for and AAA combo or a Dsmash. The AAA combo didn't rack up as much damage and the Dsmash was often too slow and got shielded by the MK. I would recommend incorporating the shieldgrab and grabs in general into your game. With the way they've been improved for Brawl (Super Armor/ "Grab" Armor), they are a great force.
Secondly, you should move your arrows. You were using them like Falco's blasters, and they were just going straight and missing often. When the MK was recovering, you could have easily tilted your analog stick to aim the arrows into him.
Thirdly, I noticed you F-smashed when the MK was in range of an Ftilt, but not an FSmash. I know I accidentally Fsmash a lot when I want to Ftilt, so maybe we both have the same problem there.
Lastly, check out the sidestep. Against MK, perhaps the sidestep is less sueful because of his many multi hit attacks, but it usually leaves you in position for counters if done well.