To check the grammar in a particular sentence

English as a Second Language English for Beginners
1

I am taking your beginners swimming classes on Thursdays.But I could not attend to the one of the classes.So can you give me a extra class for it

want to check above sentence grammatically right or wrong

2

Sorry, I missed this post. Here is my suggestion:

I am taking your beginners swimming class on Thursdays. But I could not attend to the one of the classes. So can you give me [an] extra class [in exchange for the one I missed?]