It's nice to finish your essay with a conclusion, but I'd say that the conclusion is the least important part of your essay. Don't worry too much if you don't have time to write one; your main body paragraphs are much more important.
I advise people to write short, fast conclusions. Just paraphrase the overall answer that you gave in your introduction. For example:
My introduction from last week's lesson:
Businesses have always sought to make a profit, but it is becoming increasingly common to hear people talk about the social obligations that companies have. I completely agree with the idea that businesses should do more for society than simply make money.
My short, fast conclusion:
In conclusion, I believe that companies should place as much importance on their social responsibilities as they do on their financial objectives.
Can you find examples of paraphrasing in the introduction and conclusion above?