Testosterone level should be 5-7x the weekly dose. Test should be done 6-8 weeks into cycle. Test should be taken 24 hours after last shot to get peak level results, testosterone levels will start on their way down 36 hours after last shot. Many factors are involved that affect test; age, size, bodyfat%. Being that you were only taking 750mg for 12 days you should go with the 500mg per week at 5-7x for the test levels. After 8 weeks of 750mg check your levels again and see where you are at.
Looking at your test I think you are right on par for the dose.
Thanks
TMM