ACT Subscore Fluctuation - HELP

I have now taken the test on two different occasions: first in April without any prep, and once in June with some reviewing in the week preceding the testing date. Although my composite score did improve by one point, the areas in which scores changed startled me.

April Test Date:
English - 28
Math - 27
Reading - 28
Science - 25
Composite - 27

June Test Date:
English - 26
Math - 29
Reading - 26
Science - 29
Composite - 28

This change in results was a(n unpleasant) surprise to me, mainly because English is what I consider the easiest/my best section. Although I didn’t take the time to really delve in and study, I feel very disappointed in myself as I worsened significantly in two of the four areas and am unsure of what may have caused this. I not only did better when not studying whatsoever, but did worse the second time around with a full night’s sleep, a good breakfast, etc. (not to mention that for the April ACT I got 5 hours of sleep and didn’t really eat too well). Any insight on to why this may have happened and how I can prevent this from occurring again in September (maybe how or what I should be studying) would be much appreciated.
As an extra note, I used the “Real ACT Prep Guide” to review and my final goal for a Composite Score is a 31. I’m applying to USC, LMU and Chapman for Film.

It seems to me you have never properly prepped for the ACT.

A 31 is within your reach. But just taking the test over and over agin will not get you there.

So proper preparation and allocated study time would be the biggest key?
It does seem obvious but in the little time I did go over the book, I was afraid even if I studied/prepped more it wouldn’t help my results at all.