Could you check it?
Could you, please, check my sentence or suggest a better way to say it?
Here is the context:
a person asked me if I would have free time in the evenings and now I need to explain that I was wrong and I will not have any time for the lesson in the evenings.

Here is my sentence:

Hello. I'm sorry but as it turned out I won't be available in the evenings after all.

Question

Could you check it?
Could you, please, check my sentence or suggest a better way to say it?
Here is the context:
a person asked me if I would have free time in the evenings and now I need to explain that I was wrong and I will not have any time for the lesson in the evenings.

Here is my sentence:

Hello. I'm sorry but as it turned out I won't be available in the evenings after all.

Answer

"Hello. I'm sorry but as it turned out I won't be available in the evenings after all."

Your sentence is correct.
Some alternatives:
 "Hello. I'm sorry, but I've just realized my evenings aren't free, after all."
"Hi, I apologize, but I've just discovered I'm no longer available in the evenings."
"Hello, sorry for the inconvenience, but my evenings are no longer available."