"If I ate more, I would be stronger."
Translation:לוּ הייתי אוכל יותר, הייתי חזק יותר.
I have mostly the same sentence you did and it was marked wrong. I think they wanted יותר after חזק. Also your אלו is missing a yud (should be אילו), but that should have been marked a typo, not "wrong"
Okay. From what I understand, it matches the English sentence they give better. "לו הייתי אוכל יותר" seems to be "If I was eating more" to me, according to what they teach in this course.
To add another idea to this discussion - looking at it from the opposite direction:
- "if I were to ..." feels like quite a satisfying match here.
Of course, the two languages don't always correspond with perfect precision to each other, but there can often be certain types of construction that can work quite nicely.
[EDIT] even better, although a little more long-winded:
- "If I were to have eaten more ..."