It is never a good idea to be dishonest or embellish your achievements. If you feel the need to exaggerate, then that example is likely not strong enough to discuss in your letter of recommendation. Instead, focus on areas that make you shine as a candidate.
If you struggle coming up with examples, reach out to your letter writer and see if you can compromise and work together on this one section. Perhaps your letter writer has a memory of your work that you have forgotten.