My understanding is that the window for imprinting is very small, and has passed. But that doesn't mean your duck won't be friendly and enjoy your company.
My ducks are not imprinted on me. I have 3, and got 2 as 1.5+ year olds adults. They were terrified of me at first. Now they come when I call. Follow me around. Eat from my hand. Run to me when they see/hear something scary. One even hops up into my lap. The one I got as a baby doesn't even do that!!
None of my ducks enjoy being touched, though. Out of respect, I don't do it. They also prefer it if I walk around them instead of directly toward them, and avoid direct eye contact.
It took me about 2 or 3 months to tame my "wild" adults. I was only working part-time, and it was summer, so I could spend tons of time outside with them. Basically I sat outside in the grass ( in their aviary) and threw mealworms at them. I was very very still. I spent many hours a day reading about 10 feet away from them. When they seemed comfortable with that for a couple days I sat 8 feet away. I always threw mealworms so they associated me with deliciousness. Slowly I got closer and closer, until they were eating the mealworms right from my hands. I never moved closer until they were comfortable. Patience is the key.
Even though my ducks enjoy me very much, they would be sad without another duck. For the emotional health of your duck I highly recommend you get a friend for your duck.