Don't take this the wrong way but you don't have the fundamentals down at all so before you focus on improving strategically you just need to simply: get better.
You're missing lots of fast falls, l cancels, full hopping a lot for no reason, using your double jump a lot for no reason, it's unclear if you can wavedash OOS at all, your spacing is poor, you're missing lots of jc grabs, you're experiencing fits of sidestep spam and rolling when you get into trouble, it appears you are just taking pure guesses on your tech chases and hoping you're right, etc.
Advice: Very general, but play lots of different people to gain more experience. Watch as many videos as possible of all the good Marth players (personally I watch just about all Marth players to get an idea of all the various styles). Keep getting recorded and watch videos of yourself as much as you can. Only you know completely what your thought process was on each decision you made so go back and question every wrong decision and what you could have done better. Other than that, play a lot and have fun.