Hahnsh,
You certainly have the option of paying back your full Social Security benefits received since age 65 + 4 months, and re-electing Social Security at age 70 (with the increased benefit that would be eligible to you at age 70).

However, I'm not aware of any provisions that would allow you to pay back "only" the difference between your personal benefit and what your spousal benefit would have been - since that would effectively mean that Social Security would be allowing you to retroactively claim a spousal benefit that you hadn't elected at the time.

So you can move forward with your payback and reapplication of Social Security if you wish, but as far as I know your only choice will be to pay back the full amount of benefits received.

I hope that helps a little!