Are both the same?
There's only one thing I regret.
There's only one thing I'm sorry about.And these;
There's only one thing I've got on my mind
There's only one thing in my mind.

Question

Are both the same?
There's only one thing I regret.
There's only one thing I'm sorry about.And these;
There's only one thing I've got on my mind
There's only one thing in my mind.

Answer

Hi,  yes they have the same meaning.  
The last sentance should read 'There' s only one thing on my mind. '

Hope this helps