Do you think it's OK that I once lied about a sandwich?
Why would you lie about that?
I feared my father wouldn't trust me anymore
I think it's reasonable to tell a small lie about a sandwich if telling the truth would have otherwise damaged your relationship with your father. Just make sure not to tell lies that would hurt someone.
I don't get it. It's not like I hurt anyone
Well, it is hard to fathom what harm could come from not being forthcoming about a sandwich. I'm wondering if your fear is unfounded, or if it's a symptom of a dysfunctional relationship between you and your father? If you think your relationship with your father isn't that good, you should consider talking to a counsellor about it.