You're right.
3 seconds sound clip from the Back to the Future movie soundboard.
You can hear this line at 01:08:49 in the Blu-ray version of the movie.
Quote context
[...]
- You know, there's something I haven't told you about the night we made that tape.
- Please, don't tell me. No man should know too much about his own destiny.
- You don't understand. I do understand.
- Now... Let me show you my plan for sending you home.
- Please excuse the crudity of this model. I didn't have time to build it to scale or paint it.
- It's good. Oh, thank you. Thank you.
[...]