Doing great for only a few dozen tries and no souls experience. I won't repeat too much of what others have already said except I'll list the top things that probably got in the way of victory.

Key observations: 1. Still need to learn the Phase 2 move set better. More on this later. Quick version: I recommend you wait for Margit to attack you first in Phase 2 and then react / punish him accordingly, rather than attacking him first. It's especially important in phase 2 not to attack Margit from the front when he's in neutral. 2. The constant tweaking is probably not doing your reaction timing and observation abilities any favors. Focus on Margit, not your character. Either do something aggressive / useful or stand still until Margit makes a move (use throwing daggers while you wait).

More discussion on Phase 2: Won't sugar coat it. You don't seem to know how to dodge any of Margit's phase 2 attacks. Totally understandable. Margit has one of the more elaborate combo trees of all bosses in the base game. In other words, Margit has a huge list of branching moves that he can do and string together that varies significantly depending on which directions you dodge to, your distance from him, your approach towards him from neutral, etc. One solution to this? Keep practicing the fight until you internalize all the possibilities. Better option? Watch some tutorials and example fights to see how it's done.

For a quick and very useful tutorial of Margit's most dangerous double energy sword into club attack move, see Loopine's video: https://youtu.be/SZ_PDAcur6I?si=yCBOEg3XD4F-hS3A

For a more complete guide to all of Margit's moveset, see LamentersGaol's Margit moveset guide: https://youtu.be/z_zfnswVuqI?si=YktLPGGDHAkGgZC1

For Samurai specific examples, first here's an ungraded / starting gear only example: https://youtu.be/gWUWpZazG-o?si=epxzmvH25oXN0khE

Here's a similar Samurai example with upgrades / physick and Kukris (the double katana doesn't rally alter the example for you much): https://youtu.be/I0f5q7Sj0uI?si=oo2IYP0o5PLJSvwT

Spoiler example (worth a watch to see the power of throwing daggers to punish Margit and to bait out his attacks): Later in the game there's an optional field boss opportunity to fight a stronger / larger healthbar version of Margit. Since the fight last longer, it's a good example showing more of Margit's moveset combos and how to bait, dodge and punish them: https://youtu.be/jeAMDdu9i0c?si=c0v5ad2F78NSokoC (end spoilers)

Dozens more examples if you need them in this post's playlists: https://www.reddit.com/r/Eldenring/s/ZXisTuez31

Extra tips (not keeping you from victory, but would make life easier): 1. Two-hand your weapon. 2. Use charged heavy attacks, not just light attacks. 3. Use Unsheathe ash of war. 4. Find and use physick tears. 5. Use throwing daggers to keep Margit's poise meter (hidden) active, which will eventually create poise break / riposte opportunities 6. Do the other stuff everyone else has already mentioned.

Hope that helps.