-Looks like you need to learn his jump height. There were alot of times where you tried to do an aerial attack but just didn't go high enough.
-Sonic's kill moves are precious. Fsmash is nice damage early in the game, but you want to try to reduce its stale move effect as much as you can so you can kill when you need it to kill. Same with b-air. It's got its uses in some situations, but don't use it too often. Those two moves, and dsmash, can kill from the center of FD generally starting at around 120%.
-Spring drops. It's a very underrated move, but it's oh-so-useful. Dropping a spring so that the spring's knockback leads into another attack, or to force him into a shield, is soo useful.
-I'm not sure if the missed grabs were due to lag (some matches aren't laggy - especially between two fast connections), but you definitely want to shield grab more, or like Umby said, use shield cancelled spindashes/scsd grabs.
-Also, use more side-B. Helps to mess around with timing a bit. Try using early dash attacks so that you can follow up with another move, like a tilt or aerial, instead of rolling too far and having to chase after him.