Is my suitcase tag innacurate, or am I an idiot?

I've never flown before, so I'm a little nervous about it. But I got a suitcase, and on the tag, it says it's dimensions add up to 62 inches, which is the maximum allowed for American Airlines without paying $200. However, when i measure the suitcase, i get 65 inches.
Is it possible that what the tag says is innacurate and that the airline will make me pay a fee for the extra size, or am I just bad at measuring?

We don't know since we can't see the bag.
My guess is that you didn't measure accurately.

Anything is "possible" and many things are "probable" in this case it is highly unlikely that the suitcase is wrong. Leave the tag on it and if questioned show the tag.

No airline has ever measured my luggage. If your bag looks about the right size then it will be OK. However, the weight is important, and do not exceed 50 pounds.

Sure it is possible that the tag is inaccurate, it is also possible that your measurements are inaccurate. And without seeing the bag or knowing how you measured I would default to the tag on the bag being correct. But the only measurements that count is what AA says or what you can convince them of.

You can leave the tag on, the Check-In agent may look at it and just let it go on. But since they handle hundreds of bags a day, if the size is something that makes them question it and it turns out to be oversized and you are charged you will need to pay. However, I would keep the tag as that may give you a good case against the manufacturer.

Not enough data. There's a specific way to measure it.

I'll be honest- airlines are VERY inconsistent when it comes to enforcing their own rules. The largest issue (no pun intended) will be the weight of your bag. If the weight is less than the limit you're probably fine (I've never seen someone measure a bag with a tape measure- I've checked golf clubs on Air Canada, United, Jet Blue and American and never had anyone measure anything other than weighing the bag).