This is a perennial question: can I make something up in my memoir? It would help with the drama / or the flow of the story / or salve someone’s feeling.
The short answer of course is, of course, you can make anything up that you want because it’s you story but why would you want to dilute your memoir by not telling the truth?
A memoir is the true account of a time or an experience in one’s life. Your adding fiction for the ease of the telling (or for whatever reason) is akin to lowering the net when you are playing tennis. Yes, you will lob more balls over the barrier by lowering the net but it will miss the point of playing tennis.
When you adhere to telling the truth—the whole truth—in a memoir, you will find yourself forced to consider, and reconsider, your lifestory and so come to a new understanding that fiction, even a little bit of it, permitted you to avoid. The reader may not know the difference (most likely since you are so clever!) but you will have missed the opportunity to know your life and yourself in a way that you might have known it had you not taken the easy way out of memoir writing and opted to “lower the net.”
I urge you to commit to telling the truth—100% of it—in your memoir. It’s the only way you will get to the truth—and as they say, the telling the truth will set you free.