I think it’s normal not to remember everything. There’s a lot of stuff in WK, lots of vocab words, and also lots of stuff that I’m certain I will hardly ever use. I’m at a similar level as you, and am also having more trouble with WK.
The main thing for me is to be realistic. I try to focus on the important stuff, and am currently trying to ramp up my reading through Satori. After all, the real goal of using WK is to be able to read. If you come across the kanji/vocab often, it will start to really get burned into your memory.
I personally also use an undo script. If I fail an item that I think it’s important, I really fail it and will come back soon in the reviews.
My personal nightmare are verbs. Transitive/intransitive, I hardly ever remember one or the other. I try not to pay to much attention to that. Learning a language is a long process, and if I ever need the verb or encounter it through reading, I will then learn it.
So I would really recommend you to start reading. If you want to get more acquainted with simple grammar structures, I recommend you the Michel Thomas Japanese course (you can try to find it in youtube).