I received an ACT score of 33, with Math: 36, English: 36, Reading: 31, and Science: 28. In comparison to Math and English, how important is the Science grade? I honestly just lost stamina and focus towards the end of the test 
It really depends on your major. For engineering and CS, they really like a good math score.
I’ve also heard that it doesn’t matter too much, since the ACT is mostly just an achievement test.
In general, your overall score matters more, but I would definitely recommend taking it again. I find it a bit strange that your science is comparatively low though. The science section is really just the same thing as the reading section except with scientific terms. It requires very little to none thorough scientific knowledge.