Matthew Newsome discusses kilt length in his article for first time kilt wearers over at the Scottish Tartan Museum. He states that "Acceptable kilt lenght is anywhere from the middle of the knee cap to an inch or so above the knee.

So I would interpret your kilt lenght as being OK as long as you as satisfied with wearing it slightly below your naval. On the other hand if you like your kilts to be at mid-knee, then it's shorter than what you prefer.

I prefer mine to hit at the top of the knee or just slightly below the top of the knee. It's a matter of personal preference.

Darrell