Alright, so I watched your set against Marth, and here's what I got:
1) You go for hard reads way too often. I see you trying to intercept Marth with Fsmashes, which is good occassionally, but the amount of punishment you took for missing all of them was way too much.
2) You try to force the kill too much. This is bad, especially against Marth. Forcing kills leads you to getting punished, which furthers your opponent's lead on you. We especially struggle to break Marth's zone when trying to kill him, so the best thing to do is to try and zone him and then kill him when you catch him in a bad spot.
3) Similar to the above, you try to force followups too often. You must learn when to break away and reset to neutral. We don't really follow up on Marth well because his Fair just sorta swats everything away.
4) You're not making the correct punishments for your reads.
What I mean by this is that, when you're reading that Marth is going to dash at you, then jump away, you're not supposed to try to Bair him. Maybe once in a blue moon. The better option is to Usmash, which is good because it keeps us grounded, it can kill, and it doesn't involve challenging Marth in the air. There were a couple instances, especially in clutch moments, like when you were down a little bit and could have used a kill, that I noticed this, and simply running in and Usmashing the **** out of Marth would have been the best option.
I was going to comment about how you weren't properly zoning Marth, but you did a much better job game 2 than game 1, so I don't have much to say. Just learn the better options for your reads and you'll be able to clinch the win away from him. The games were pretty close, and it looked like you were just sorta struggling against Marth moreso than losing because of your own inability to beat the player.