I will practice on what I have been studying.← Is correct!

I have to study English hard in order to go to USA.
I have a time enough to study English, but I was too tired to study yesterday.



sorry,I have to go out .
See you tomorrow!

Original:

I will practice on what I have been studying.←is it correct?

I have to study English hard in oder to go to USA.
I have a time enough to study English.
But, I was too tired to study yesterday.


Revised:

I will practice what I have been studying.

I have to study English hard in order to go to the USA.

I have enough time to study English, but yesterday I was too tired to study.

Suggestion:

I will practice on what I have been studying. 

I have to study English hard, in order to go to USA. /In order for me to go to USA, I need to study English harder. 

I still have enough time to study English, but yesterday I was too tired to study.

Sorry, I have to go (out) now.
See you tomorrow!