Don’t bring yourself down too much! The first step is to realize you made a mistake, so now you can work on reversing it.
On the bright side, you’re at level 12, so you’ve been exposed to (edit: I counted properly this time!) 425 kanji. That’s more than what’s covered in the two Genki textbooks (317) which is about 2 years of Japanese study at a university. Not bad considering you reached your current level in a year! It’s more than enough to get your feet wet and get started with a textbook or work through more basic reading practice via a graded reader. Even if you only remembered half, that’s still more than the equivalent of what you get in one Genki textbook.
How much Japanese grammar do you know? If little to none, that’s no problem! Some people will use videos on Youtube to learn grammar, others will use textbooks. I don’t know about the other textbooks, but I like Genki because you’re following the story of a foreign exchange student in Japan and her dialogue exchanges with different people in different situations. And in those dialogue sections, you’re introduced to a new grammar point (as well as vocab and kanji), and they’re explained pretty well I think. At your level too, you should’ve learned most of the Genki kanji that it covers.
If you’re lacking the motivation to move away from WK, try joining one of the book clubs like the (Absolute) Beginner Book Club. There’s also read every day challenge, extensive listening challenge, etc. where you can help stay accountable for your studies by posting for all to see!