Issues with scrolling

So I play Jack, and I would like to use the skills Incentives and High Frequency Trading but the game seems to hate me. I, like many pc players, like using the scroll wheel to swap my weapons but every now and then the game gets weird. Instead of scrolling down and swapping from weapon 1 to weapon 2 i scroll down and swap from weapon 1 to weapon 4. This has never happened to me in borderlands 2 or any other games. If someone knows what’s going on and how I can fix it, thanks in advance.

PS If it helps, I’m playing on an apple computer