The thesis statement should capture the main idea of your paper, plus it should express your position. Be careful not to bury it in the middle of your paper. It's the opening guide for the reader, and it can help you as you write to keep focus. However, it may be that your thesis statement needs refining as your arguments within the body of the paper evolve. Avoid using words like "In this paper I will..." Just get to the point clearly.
The concluding paragraph is different from the opening paragraph. That's why the "cut & paste" didn't work. The conclusion will restate the main thesis, but in addition it will give a recap of the most important points within the body of the paper. Finally leave the reader with a lasting impression in your conclusion statement. Avoid "In conclusion..." Hint at things to come, broader implications, etc.