People ask me all the time how long it took me to learn all the drink recipes I know and to feel 100% comfortable working behind the bar. When I first started working behind a bar, I didn't have a clue as to what I was serving. I picked up all my knowledge on the job. The person training me told me that I wouldn't feel comfortable working behind the bar for at least six weeks. He was right.
If a customer ordered something, I would have to stop and ask the bartender I was working with for the recipe. Then I would write down the recipe in my own bartender bible so I would have it for future reference. Sometimes, I would even have to ask the customer how to make the drink they were ordering. Thankfully, I had customers that loved showing me the ropes. They got a kick out of teaching me how to make their cocktails the way they liked them. Hey, the customer can be right in some situations. ;)
Honestly, the only way I really learned all of the drink recipes over the years is thru repetition. Making those same drinks, over and over again. It's the same thing as when you start bartending at a new bar and need to learn the bar's specialty cocktails. After you make the same drink a few times, the recipe clicks in your head and becomes engraved up there.
Nowadays when I start working behind a new bar, I don't feel 100% comfortable for about a month or so. Every place has their own way of doing things and their own way of making things. Just because you learn something one way at one bar, doesn't mean it's going to work for the new bar. You always need to allow for time to adjust to those new ways at the new place.
Just when you think you know all there is to know about bartending, you start at a new bar and feel like the new kid all over again. At first I hated that aspect of bartending, but now I am learning to love it. It helps you grow into a better bartender.
Expand those horizons and get out of your comfort zone.