I don't understand why science is graded the way it is.

I am completely confused why science is so punishing for missing a few questions. Math and writing are graded on percentage (a 55/60 on math = 33/36 because the percentages are the same) while reading is graded a tad bit more leniently. I’ve been pulling straight 28s and 27s on the science section on practice tests. Maybe it’s because I’m a first time act test taker and I don’t understand or maybe it’s because I’m anxious and confused but I dislike how act science is graded. (I’ve been getting 30s, 31s, and a few 32s on practice tests)