Well first of all if you lost this easily you must understand that it will take a long long time until you reach his level. I'd strongly advise you to get some sort of coaching to have someone who may spot errors in your technique. Paul's coaching weekends are one very good way of getting at least coached once.

If you don't have access to a coach, film yourself while playing and then compare and check with badminton technique videos. This way, you can basically coach yourself.

Otherwise gingerphil suggested what you must do to fix certain areas of your game. I believe it's best to focus on doing dropshot drills in one session, then smash drills in the next one and not to do all the shots in one session. Besides technique, work on footwork and general fitness.

Hope I can help 😉

It sounds like you already have a coach. Have you discussed with him/her what your goals are and the timeframe (and whether this is realistic)? That conversation will be more insightful than a post on this site where we don't know your game.

In addition to lessons with your coach, do you have a training partner? Do you do speed and strengthening drills outside of your lessons? Do you play against a mix of skill levels and styles?

Based on what you've said (and the score), you've got quite a bit to go to get to that opponent's level. To get there, you'll probably need to devote a lot of time and effort; good luck!