I haven't made a decision yet what to do.

应该是I haven't made a decision yet on what to do.
或者I haven't decided what to do.
decision名词后面多用介词on,如果是动词的话就可以直接接what从句了：）

I haven't made a decision what to do yet.

I haven't made a decision yet on what to do.
或者I haven't decided what to do.

我还没有做出任何决定,怎么办?
I haven't made a decision yet on what to do.

I haven't make a decision yet,what i'm going to do.