Generally speaking, you want to score decent enough on the IR section so as not to draw negative attention to a low IR score
You don't want the admissions committee to focus on a really low IR score of like 1 or 2 -- that shows lack of effort or ability
That said, it's not that much more beneficial to have a perfect 8 versus a 6 or 7.
So ideally, you want to stay in the 4, 5, 6, or 7 range to efficiently get a score that is decent without putting a crazy amount of effort.
Now, with your IR score of 3 -- well, that's kind of cutting it. However, your 750 score is high enough that it'll offset the IR score of 3. So in your situation, I wouldn't worry about it.