The Butterfly Effect Proving time travel

Quite rightly, Ashton Kutcher s cell mate in jail doesn t believe in his boasted time travel skills. So Kutcher goes back in time, sticks a skewer in his hand and then in the present shows off his scars which blows his cell mate s tiny mind. Except, wouldn t those scars have always existed in this new reality considering they had already happened in the past before prison? So the cell mate would just think he was showing him old scars. Hmm, this means you can never prove, or disprove, time travel. In that case, I can definitely time travel I ve just done it.