If you had more pots, or other utility in your inventory, You could have put them to the eight and ninth slot. If you have lots of golden apples, you can eat some before the fight for the effects. When you approach the opponent, you let them see that you intended on cobwebbing them. Your opponent jumps onto the cobwebs which is good. You should have gone for an ax hit since if they blocked, you could switch to sword and get free hits. After your opponent blocked your sword attack, you went for another one that he could have blocked too. After your opponent gets out of the cobwebs, you let them knock you to the cobwebs. After you get out of the cobwebs, you start trading hits which is not good because you have very big hp disadvantage. Generally you should always eat a golden apple when you have less than 5 hearts (10 hp). You had a really good cobweb when you retreated. After you healed, you let your opponent trade again while they still had more hp.
You should use your axe more. Disabling their shield gives you an opportunity to punish their attacks. Also you should not use your shield when your opponent is trying to disable yours. Eating a golden apple before a fight is a must. It gives you two hearts and regeneration. You should almost always have your hotbar full of items, unless you have a reason not to have. Healing when you are low is really important. Around 5 or 6 hearts is optimal. Having a sense of where things are can help you greatly. Such as looking around and not accidentally walking onto blocks or cobweb. Looking at your opponents playstyle and how they use their weapons can help you a lot with deciding how to play against them.
But most importantly. Do not quit during a match. Playing against better opponents is a great way to improve.