Should inner tube have excess length?
A tube should not have excess length, and doubling on itself will cause the tire to feel uneven while riding, as well as increase the likelihood of flats.

Assuming the tube is the correct size for the tire, as you said it was, there are 2 common causes for this problem.


If you installed the tube without inflating it first, just a tiny amount, then it hasn't got the shape to sit in the tire completely, and it will appear to be too long. It isn't, just add enough air to the tube to give it a little shape and try it again.
If you did that already, then in the process of inflating the tube to make easier to install in the tire, you have probably inflated it too much, and so it has gotten larger. It's not permanent, just let the air out and inflate it only enough to give it shape before installing it in the tire.


If these don't work, there is likely a problem in manufacturing, and you should get the tube exchanged.

Hope that helps.