UILabel 设置字体大小不一

NSString *str = [NSString stringWithFormat:@"￥%@",model.total];

    NSMutableAttributedString *mutStr = [[NSMutableAttributedString alloc]initWithString:str];

    NSRange range = NSMakeRange(0, 1);

    [mutStr addAttribute:NSFontAttributeName value:[UIFont systemFontOfSize:13] range:range];

    _offSetLabel.attributedText = mutStr;