我恐怕不能（这是一句口语 很常用）i'm afarid not 才对
afraid
[英][əˈfreɪd][美][əˈfred]
adj.
恐怕; 害怕的; 担心的; 畏惧，害怕;
例句
I'm afraid I can't help you.
恐怕我帮不了你。
afraid 用法
一、be afraid of doing sth的用法
(1) 担心会发生某事或某情况(但实际上未必会发生)。
如： She was afraid of waking her husband. 她怕吵醒她丈夫。 I was afraid of hurting her feelings. 我怕伤害她的感情。
注：be afraid of doing sth 表示担心会发生某事或某情况时，其后也可用 be afraid that 替换。
如： He was afraid of losing face. ＝He was afraid (that) he’d lose face. 他怕失面子。
2) 害怕做某事或不敢做某事(指缺乏勇气或害怕其后果而不敢)
。如： I’m afraid of telling her. 我不敢告诉她。 He was afraid of jumping. 他不敢跳。
二、be afraid to do sth 的用法 be afraid to do sth的意思是：害怕做某事或不敢做某事。
如： He was afraid to fly in a plane. 他不敢坐飞机。 He was afraid to go into the house and meet his father. 他不敢进屋去见他父亲。
温馨提示：答案为网友推荐，仅供参考