Flowery pronunciation

I recently taught a lesson on flowers, their parts and how they are the reproductive organs of the plant. It all seemed a straightforward lesson until one of my students read a word from the flower diagram.  I showed a picture on a powerpoint slide of a flower. There were arrows pointing to different sections of the flower and the  Ss had their TB's open with a named flower diagram in it.  My S read the word as  "pee tahl". This is L1 interference as he has a mental connection (pe = blood or rain, and al would have an ahl sound like "ahl bap" a spicy meal).
I corrected his pronunciation and got the class to repeat "pet  ull", but then I looked down at the diagram to see the word "sepal" (the green leaves that protect the budding flower) on the diagram as "petal"  which for all intensive purposes has the same kind of  form  (Consonant) CeCal, then I thought about the place name "Nepal" which has a completely different pronunciation as well.  Honestly, I have rarely if ever used the word "sepal" before but I knew that it was not pronounced in the same way as petal.  I wasn't 100% sure of its pronunciation, but it turns out I was a good guesser :)

My problem now is encouraging my Ss to be excited about learning and speaking English when there are confusing pronunciations like this which would activate their affective filters, and have them clam up.   I need to focus my preparation and think like my Ss so that I don't gloss over aspects of the lesson, thinking they would already know that, or know how to pronounce it.