What type was the carpet you bought? Did you guys get a Darwin or IJ? Those two that I mentioned are on the smaller end according to most sources.
My coastal X is 2 years old in 5 days. She is about 6 feet long and looks like this:
The photo is about 2 months old so she a bit longer now.
She is more than likely crossed with jungle or diamond.
She is still relatively slender, and is a bit thicker than a garden hose in some areas. I feed Large rats, quail, and chicks.
Contrary to what some folks think, carpet pythons are capable of taking HUGE prey items without any issues and as mentioned above if the previous owner was feeding small prey, the growth of the snake will be much slower.
Growth rates are different with each individual snake and you may want to ask to see the parents of your snake to see the potential adult size.
This is the mother of my snake. This photo is already about 3 years old and the breeder's girlfriend was holding her up here to show her size.
I'm told now she is close to 9.5 to 10 feet long, but that is still a slender looking snake IMO.
You should take a few photos, but there isn't a reason for concern at this point unless you see a glaring issue. If you bump up prey size you will see increased growth. If you are having issues with transferring to rats, try to scent the rats with chicks or quail prior to feeding. I had to keep some of my frozen rats in a bag with frozen chicks to get my girl interested in eating. My snake has been and can still be picky.
The weight of carpets comes with proportional growth so if you still have a short snake, the weight normally won't be much.
I recommend the book THE COMPLETE CARPET PYTHON I think that will give you an understanding of the Morelia group.
Get your snake feeding once settled and it will grow.