Sour Mash issue

Two part question here. The first is that I'm trying to brew a Berliner Weisse using a sour mash technique. My recipe is a 10 liter batch using 1kg of wheat and 1kg of Vienna. I'm doing a BIAB so Beersmith asked for 14 liters of water for the mash. I didn't notice and added 15 liters. The pre-boil gravity was supposed to be 1.036 but mine came out at 1.020

Question 1: Would a liter cause this drastic a change?

The second thing is that I am doing a sour mash. So I added the lacto (sourdough starter) and let it sit till this evening, 36 hours. I measured the pre-boil gravity and it was sitting at 1.012 so in that time the yeast had already got to work. I thought the boil might bring it up to 1.030 or so, it went into the fermentor at 1.016

Question 2: What would I need to change to have the pre-boil gravity reading still be a bit higher as the sourdough starter for the lacto already converted some of the sugars? Am I missing something here in my calculations?

Just want to know if adding DME at this stage would be an option

I don't have an answer to your questions - sorry. But I do have a recommendation for the next time you try this:

http://www.basicbrewing.com/index.php?page=november-21-2014-sour-wort-berliner-weisse

I follow this general recipe and technique and make some great beer. It's pretty easy too!

Thanks for that. I just want to know what I did to mess up so badly. Seems something went wrong that normally doesn't. First time that this has come out the mash tun this low for 2kg of grain.