I am not really knowledgeable about US stamps, especially of that era (nice stamp) but if it was Canadian I would call it Fine to Very Fine with Jumbo-sized side margins.
So, in other words, yes, it is reasonably well centered. To me, anyway. This new grading system of percentages is beyond me.
ZhangCheng, could you look at this thread about the Canada Year of the Tiger stamp and tell me what the Chinese characters on the center left, center top and center right selvages say please? Thank You. Post it in that thread if you answer. Thanks.
https://goscf.com/t/6799