the shoes don't fit me.They're either too big or too small.这一句是正确的.
“这些鞋我穿不合适,不是太大就是太小了.”
the shoes don't fit me.They're neither too big nor too small.
这句话的意思是“这些鞋我穿不合适,既不太大也不太小.”前后矛盾,不通顺.
希望能帮到你,祝你开心.