Is there a difference between turning to Allah in repentance and turning to the the Lord in repentance?

There is no difference between saying "repentance to Allah" (al-inabah ila Allah) and "repentance to the Lord" (al-inabah ila al-Rabb), because Allah is the Lord, the Sovereign, and the Disposer of affairs. "Al-Rabb" (the Lord) is one of Allah's names, and it is not used for anyone else except in a possessive construct. And "al-inabah" (repentance/turning) means to repent, to feel remorse, and to return.