下载了中领馆的“单身证明书”文件? - Could you provide a link to such document?
I checked NYC general consular, and found info below:
应提交的其他材料:
１、声明书文本；
２、离婚的，应提交离婚证或离婚调解书或离婚判决书原件及复印件；丧偶的，请提供原配偶死亡证明原件及复印件。
具体要求:
1、当事人应有完全民事行为能力；
2、当事人亲自申请并在领事官员面前在声明书上签字；
3、婚姻状况声明书公证的有效期一般为六个月；
4、未婚人士如处理房产、办理户口等事项需申办无配偶声明书公证，应在声明书中说明此证明仅限用于在国内办理相关事宜；
５、有特殊情形的，应根据使领馆要求办理。
公证常见问答 - （二）旅居国外的华侨回国结婚时，应当办理何种公证？ 根 据《婚姻登记条例》规定，华侨在国内婚姻登记机关办理婚姻登记应当提供本人无配偶以及与对方当事人没有直系血亲和三代以内旁系血亲关系的证明，该证明可由 居住国公证机构出具公证、经中国驻该国使领馆认证，或者由中国驻该国使领馆出具公证。建议旅居国外的华侨回国结婚时提前办妥相关证明。未婚公证自出具之日 起6个月有效。
Not having seen your mentioned 单身证明书, I believe when you have such document not notarized, you could still require "或" - to be notarized by "由中国驻该国使领馆出具公证".
When you fill the 单身证明书, only sign/date it in front of a notary, it will be stamped (refer to 公证书). If no space available on above document, print it on leagl size paper to make more room. This is "可". In case this document needs to be sign in front of consular officer, just sign it again.
中华人民共和国驻外使领馆公证认证申请表 - It looks to me to bring this completed document and sign in front of consular officer. It does not appear it requires notarization.
