As long as you're not going through LAX where they tend to actually enforce some of this stuff because their flights are so crowded, I wouldn't sweat it.

I carried all sorts of bizarrely sized and shaped packages on both domestic and international flights during my semester abroad and the summer afterwards, and the only remark I got from flight staff was when I had a giant falling-apart plastic bag of Oud (Egyptian guitar) and Nubian basketry that would only fit in an overhead compartment at the waaayyy front of the plane whilst I was seated in the waaayyy back. The trio of flight attendants peered in at it after all the other passengers had shuffled out and said something to the effect of "Oh, it's a...sombrero, or something."

You'll be fine. :D