First, welcome to the forum. You will find many on here who have tons of information and experience. If you scroll down the screen, you see a "hunting" section, which is where you should post further questions about hunting. The forum managers will guide you further with that.
As far as the shotgun, if it has screw in chokes it is not rifled. They do sell rifled barrels for shotguns, some of which are "cantelever" or with the top of the barrel extending back to accomdate a scope. That way you can take the barrel off and keep your scope zeroed in. The cost of a cantelever rifled scope is probably cheaper than buying a new rifle. However, you can use your regular barrel to shoot slugs, you just won't be as accurate at greater distances. I took a nice doe last year using a youth model 20 ga. shotgun with a modified choke in my barrel, but did have a scope on the gun. I think the key is practice with what you have. (If you missed a couple turkeys, you may want to practice estimating distance and shooting.)
In the state I live in (Delaware) you have to use a shotgun for deer. I normally use a 11-87 Remington with a cantelever (sp?) barrel and a 4 power leapold scope which I shoot slugs through. It seems to me that each gun handles different slugs differently, so we are back to practicing with what ever you use. Some people shoot slug guns out to 200 yards or so, I shot most of my deer under 100 yards.
I could go on for hours, but others on here will offer you more ( and maybe better) advice.
My biggest suggestion is you take a hunter safety course, always keep safety in mind, make sure you know the rules and regs of where you are hunting, always hunt ethically. My second suggestion is by all means continue your education until you find what direction you want to go in life.
Once again, welcome aboard. Keep us posted on how you are doing.