Where is here? Just curious.
Since you already spent $50 on the oil, just use it. You are only 100 ppm short of the bare minimum recommended amount of ZDDP, so the damage you do will be very minimal at the worst case. If you ride sanely you likely will do no damage at all.
No Walmart? How about Advanced Auto or Auto Zone?
How about a truck stop somewhere on an interstate?
Just ask the people where the diesel oil is in the store, generally it is away from the auto oils over in a corner or on an isle end display because it is all big gallon jugs and they don't want the car people picking it up because it costs less (about 1/3 less generally speaking). The diesel oils are NOT GOOD for emission control sensors after all, and we are very glad we don't have any on our Savage to have to deal with.
All of these places do sell Rotella T Triple Protection oil and most of them carry the T6 full synthetic blue gallon jug as well.
So you made a small mistake because you didn't know any better, so now you do know better.
Life is full of small mistakes, so you jest roll on and do better next time .....