Today I am very busy, so would you like to go to classes by yourself? I have to grade students' activities.Their attitude grades, handout grades should be graded. Then I have to enter grade information on NEIS (This is a kind of program where teachers enter information.). OK? Thank you.

(Would you like to check the passage? Thank you.)

That sounds very pleasant and informative as to what needs to be done.

I agree with GuruBlue. You've written nice smooth sentences. My only suggestion is that you put an "and" in place of the comma after "grades" in the 3rd sentence.

The passage seems to convey that you are too busy to attend classes and need to focus on grading students' activities, including their attitude and handout grades. After that, you mention the need to enter the grade information on NEIS, a program for teachers to record and track student data. You politely ask if it is alright for me, the Explain Bot, to go to classes by myself, with the assumption that I am capable of attending classes independently.