What can I say man?
You didn't space at all.
And you need to learn the G&W matchup.
G&W's bair (nor any other aerial) is not a problem for Marth. You can dolphin slash out of it, especially from a shield. Jabbing it is pretty good as well.
But about the spacing, you'd just jump into his attacks. G&W doesnt have fantastic range and his attacks are slow. You should be always able to keep yourself safe and out of his range.
-> YOU barely ever used dtilt.
When you got hit by '9' at the end, it's because you BADLY spaced your fair and jumped straight into it.
Spacing techniques involve appropriately using your dtilt/jabs, and RETREATING your fairs.
At the start (like 0:00-0:10) you were retreating fairs, but you weren't even "within the opponent". But the motion you were doing, while AIMING for the enemy is what you need to work on.
But yeah, just about everytime you were shielding, G&W would attack it not caring, as you never punished with DS. Be smart with it, don't spam it, as you get better at spacing you'll rely less on shield->DS tactics.
If you have any specific questions I'm more than happy to answer.
ALSO, God ****, at many points during the match you would just do roll, after roll, after roll, without (in my perspective) much conscious thought put into it. Rolling with Marth isn't too safe, nor productive in most cases.