With distilled water, it's almost impossible to believe your mash pH was over 5.8 or so, depending on your grainbill. I use RO water (about the same mineral and bicarbonate as distilled) and without any additions at all my very light colored lager would be about 5.8. With some crystal malt, it would probably be about 5.5 or so.
Gypsum is NOT for pH control. It adds calcium and sulfate to your water. Calcium chloride adds calcium and chloride. If you want to not do much with your water, you could use 5 grams of calcium chloride to your distilled water for some calcium and a bit of help with flavor (keeps the beer from being too bland). For a very happy beer, you can add 5 grams of gypsum in addition.
For pH control, you'll want to use an acid like lactic acid or phosphoric acid. But I do believe your pH reading is very suspect and so would probably consider not adding anything based on that.
I suggest trying our water calculator (basic one) and while there is a learning curve, it's pretty easy and can help point you in the right direct.
Also, I think that our explanation of water additions may really be helpful to you:
https://www.brewersfriend.com/2017/11/19/brewing-water-basics-part-1/