Gabriel,

If you start at zero salt, and want 3000 ppm salt for 38000 gallons, you need approximately 954 pounds of salt.

Try this calculator: http://www.poolcalculator.com/

That would be about 24 bags at 40 pounds each. Since you have put in 8 bags already, factor that in. I would also try not to overshoot, so go in smaller steps. Getting some salt test strips, or pool store testing might also be options. Just remember the same sample tested different ways will yield surprisingly big variations, so this is not an exact science.

Good Luck!
Jim