I need the money as soon as possible.

soon 不能直接修饰 need，句子需要修改一下：

I need to get the money as soon as possible. （让 soon 修饰 get）

如果非要补充的话，就要真正弄清楚这个比较关系，演变如下：

1. I need to get the money soon.

2. I need to get the money as soon as possible.

3. I need to get the money as soon as it is possible to get it.

句3，就是补充完整的句子。此时 it 是不能省略的，因为它是从句的主语。比较项是作状语的副词 soon，从句是完整的，只要不出现 soon 即可。
 it is possible to get the money soon.  这句话没有错误，那么，上面的补充就是合理的。