Its only natural to mix some kanji up, it happens to everyone so dont fret.
Luckily the system is designed to keep em coming untill you can distinguish them.
The usual lesson limit strategy is to set a maximum number of apprentice items allowed. Commonly this would be 100, which is my personal approach, but any number that works for you is best.
Another popular one is to only do x amount of lessons every day (10 for example) to limit the new item influx.
The alternative is to specifically target those items as selfstudy and dont change your general approach, but this requires a bigger commitment and more time spend.
Ive personally started using the leech trainer to deal with those pesky ones, as it seems like a quick and easy solution. (I still need some more time to evaluate whether this works for me)