I definitely found Doraemon surprisingly difficult for a long time, so you’re not alone!
The problem is that native Japanese kids might not know that many kanji yet, but they’re going to understand tons of casual speech and puns and stuff and Doraemon is filled to the brim with those, but if you’re studying with Wanikani, there’s a good chance your strengths will be just the opposite!
Also, Doraemon is just very wordy. I found it hard to get through and love a page like this:
… until I was more comfortable reading in general.
So I’d recommend, if you haven’t already, taking a look at the “resources for starting to read Japanese content thread” here:
Some common reading starting places that don’t have the obstacles I mentioned with Doraemon include graded readers, Yotsuba, and Flying Witch.
Grammar, and also just reading practice are going to go a long way, and you can use Doraemon as a motivator for now, and fun thing to read in the future!
Good luck!