honestly, to be honest

I don't agree.

私は同意しません

To be honest, I don't agree.

私は正直言って同意しません

To be honest, I don't fully agree.

私は正直言って完全には同意しません

To be honest, I don't fully agree with that proposal.

私は正直言ってその提案に完全には同意しません

To be honest, I still don't fully agree with that proposal.

私は正直言ってまだその提案に完全には同意しません