According to my UCD, professional winemaker friend, wine is microbial stable at 3.8 pH, with the proper SO2. I wouldn't touch it, or do bench trials first (although I realize you already added it). Wine has strange buffering capabilities, where it could take a lot more than you wouldd think to move the pH needle.
All my red wine turned out over 4.0 pH this year, that was Grenache, Syrah and Cab Franc (meter is calibrated and double checked with another meter). Even a 1/2 g/l of tartaric negatively affected the wine. I'm keeping the barrel topped and the SO2 levels around 70ppm. The CA state limit is 350ppm and I'll be below that, and I don't believe there will be any sensory impact, or at least I'm praying. It may not be a wine that keeps for 10 years, but it tends to be drunk within a few anyways.
So, I wouldn't worry about a 3.8 pH and if you did put in too much so2 by mistake (which I suspect), give it a good splash rack, it will blow off most the time.