'reflect back on' or 'reflect on' some event in the past?

I find myself reflecting on the journey.

In this sentence, we don't know when the journey happened. We could have

As I sit on this train, I find myself reflecting on the journey that I am undertaking right now. (present journey)

As I sit in this café, I find myself reflecting on the journey that got me here. (past journey)

Sitting at home, I find myself reflecting on the journey that I will undertake next Summer. (future journey)

In English, and most European languages, the past is considered to be behind us. We look back to the past and we look forward to the future.

In this context, "reflect" is almost synonymous with "think".

4. VERB When you reflect on something, you think deeply about it. We should all give ourselves time to reflect. [VERB] I reflected on the child's future. [VERB + on/upon] Synonyms: consider, think, contemplate, deliberate

https://www.collinsdictionary.com/dictionary/english/reflect

Thus, "I think forward to the journey" means the journey is in the future and "I think back to the journey" means it is in the past.

Answer

I find myself reflecting on the journey that has led me to where I am today. (This is correct)

I find myself reflecting back on the journey. (This is correct)

I find myself reflecting back on the journey that has led me to where I am today. (This is tautological because the past is indicated in two ways, (1) "back" and (2) "has led me")