IIRC, my largest discrepancy was 7 points, e.g., 1.090 increased to 1.097. You also need to take into consideration the final volume, e.g., if you're over by 1 quart, that reduces your final OG by another 4 points.
With the exception of H2S, winemaking requires a long view. Your SG dropped another 2 points and everything is looking good. Let the wine bulk age for 3 months, then taste. If it tastes good to you, then you've succeeded.
Don't focus on the numbers, as the numbers only tell part of the story. I have 684 lbs of grapes arriving in a few weeks -- I don't yet know the delivery date, and I have no information regarding the brix, TA, or pH of the 5 varieties in my shipment. When the grapes arrive I won't know the brix, TA, or pH until I test them myself, and from there I'm making it up as I go. That's not me making a joke or being facetious -- it's literally true.
Keep in mind that winemaking is an art. Anyone who believes it's a science is fooling themselves. Wine is the result of numerous natural processes that we can possibly guide, but not direct.
WE makes good quality kits, and your process sounds fine. Things may not turn out exactly as you expect, but you will produce a good result. Accept that Mother Nature, Dionysus, and/or Bacchus are in charge and you're just along for the ride, and enjoy the journey.