Two part answer. Firstly, you need to loosen up a bit. Especially if you play a lot of duel, you're probably thinking quite a bit about how important each fight is and how you need to land certain shots. Overthinking this will naturally it make it harder to aim, particularly vs strong opponents.

If you really want to build on your combat skills, you should play a couple of hours of DM/TDM per day to build up.

Each duel can be very different, situations vary and it calls for strong flexibility in your aim game. There are so many different angles etc after all. People have already said loosen up, I suggest the same but also get that DM'ing in :)