Why can't my ranger use guns?

When I first created my character, I had the assault rifle looking thing, but then I did a story quest and that weapon was gone and I was left with the saber type thing that can also shoot, but I really want to use that other gun. I still have it in my inventory but there's an X next to it and it refuses to equip. :(

you don have enough stat to equip it i think

After reading through some of the menu translations, I think I've figured out that I may have accidentally changed my class to hunter. I didn't know class changing was a thing.. Thanks anyway though. ^^