I need some help

There will always be a backlog of vocabulary on level up, but you can reduce the number by spreading the kanji lessons of the second batch (the ones unlocked after guruing the radicals) over several days, instead of doing them right away. It will lengthen your levels, because you only level up 3-4 days after you’ve done lessons for 90% of the kanji, but you also have more time to spread your vocab lessons.

You can achieve this by setting lesson settings to random (or ascending level then random, if you want to do last level vocabulary before touching the new level items). I personally have switched back and forth between settings to do radicals after doing last level vocab, then doing kanji and new vocab randomly over the next couple days, until the radical guru. Then switched back to ordering by type, to do the newly unlocked kanji first, then the vocab over the next couple days. This means that over the next couple days kanji from the first batch will guru, and I can do those vocab, too.

Or you can install a userscript like [Userscript] WaniKani Lesson Filter, in order to pick and choose what kind of lessons to do thst session. I am mainly using this method now to do radicals first whenever I leveled up (or the next morning). I usually don’t do too well remembering a lot of kanji only, so I mix it up with 8 kanji+12 vocab per session, only once a day, until kanji run out. Then I just do vocab, obviously.