As with most software, Bru N Water is a "dumb" calculator and doesn't suggest that you add any acid in your mash. It's your input that influences those conditions. GIGO garbage in / garbage out.
Add the oats to your recipe as a base grain and check your water volumes.
1.75mg/G of Calcium Chloride is a bit in excess, did you mean .75 mg/G?
On tab 3, set the amount of acid to 0. Check the mash pH on tab 4. If it's too high then add small amounts of acid until you reach a reasonable pH, if it's too low either add some alkalinity, remove some of your water salts or leave it alone.
Posting a screen shot of tabs 2, 3 and 4 would help troubleshoot.