Your math is wrong. I used your numbers in your OP. Now shut the fuck up and stay shut the fuck up:
41,600,000,000 ÷ 5,140,000,000,000,000 = 0.0000081 or approximately 8.1 × 10⁻⁶.
0.0000081 × 100 = 0.00081%.
The volume of Lake Superior is approximately 2,900,000,000,000,000 liters (2.9 quadrillion liters).
One teaspoon is about 5 milliliters, which is 0.005 liters.
0.005 liters ÷ 2,900,000,000,000,000 x 100 = 0.00000000000017%
So, one teaspoon of Lake Superior is approximately 0.00000000000017% of the lake's total volume.