You are so lucky/fortune today that the teacher didn't see you while you smoking. But I'm sure one day you are going to be caught up and you will get severe punishment.
Today you escaped/saved from the teacher sight while you dozing off in the class but one day definitely you are going to be caught up.
Please correct my sentences. And also suggest me a good version for the same.
In the first, 'fortune' is a noun- you could use 'fortunate' instead.
will get severe punishment- I'd used 'will be severely punished'
I'd change the second quite a bit to something like 'the teacher didn't notice you dozing...'