Don't worry, lots of people do that. If you learn a word in its mutated form first, sometimes you think that is the original word. Learners often get the following words wrong: cyrraedd "arrive", gadael "leave", galw "call", prysur "busy" - those are the original unmutated forms.
You might be interested to know too that in Ceredigion, there actually is a "double mutation": pobl "people" becomes y bobl "the people" in standard Welsh, but the Cardis mutate it again: y fobl!
No wonder my husband has to go out volunteer litter picking on our estate here in Cardiff; it's all these daft people who follow DuaLingo's advice! Please, don't throw your apple, unless it is into a litter bin. In which case Duo should be teaching us to complete the sentence with "in the litter bin"
In the next version of the course we will more words to do with recycling waste:
- Rhaid i chi daflu'r craidd afal ar y domen gompost yn hytrach nag yn y bin. - You must throw the apple core onto the compost heap rather than in the bin.