Carnival does provide shampoo along with several other sample type items (razors,toothpaste etc) that you will find in a basket on your desk/counter in your cabin.
However, if your like my wife, the shampoo they provide will not be acceptable and you probably should bring your own. If you pack it in your checked lugage, there won't be any problems. The problems occur when you pack it in your carry on luggage. My wife packs all her "necessities" in a giant baggie(in case of breakage) in our checked luggage and we've never had an issue.
Have a great cruise and welcome to C/C.