聞きたいのは、3つ全て完璧？どれか不自然？他にも案ありますか？という点です
On a ten-point scale,my rating would be 8.
If scored on a ten-point scale,it would receive 8 points.
If I were to rate it on a scale of 1to10,it would score 8.
If I were to rate it on a scale of 1to10, it would be an eight.
この場合、次のような言い方ができますよ。
ーIf I were to rate his looks on a scale of 1 to 10, I would give him a nine.
「彼の見た目を10点満点で評価するなら、彼は9点だな」
on a scale of 1 to 10 で「10点満点で・10段階で（採点すると）」と言えます。
ご参考まで！
カナダ 
