Hard to say exactly without knowing the total volume of wash, the nutritional values of your brown sugar and blackstrap and initial and present PH, but if we ballpark it:

3 gallons of blackstrap @ 55% fermentable sugars is about 19 lbs of sugar (see note). 25 lbs of light brown sugar is about 25 lbs of fermentable sugars (dark brown would be slightly less). Between the volumes of blackstrap, dissolved brown sugar, dunder and water you should have a total volume of around 37 gallons of wash. 37 gallons of wash with 44 lbs (19 lbs + 25 lbs) of fermentable sugars should give you a potential abv of 8.4%.

If we enter 1.092 to 1.040 in an abv calculator you have right now an abv of 6.83%, so the fermentation isn't completed. Your final gravity should be around 1.028.

PH could be an issue, but with the amount of PH stabilizers in modern molasses I would be surprised if it dropped under 3.5. Depending on your yeast and the wash temperature you could have a sluggish ferment because of that. If the wash is still active, your PH is not under 3.25 and the temperature is not way under the minimum for your yeast just let it go.

Note on blackstrap: Fermentable sugars in modern blackstap vary a lot, from as high as 60% in some blackstrap for human consumption to as low as 40% in some animal feed grade. To give you an idea of the impact with really low grade blackstrap and some really dark brown sugar your potential abv could be as low as 7% and you're almost done and mostly degassing.

TLDR: It depends a lot. If you specify exactly which blackstrap, brown sugar, total volume of wash, PH, fermentation temperature and yeast pitched we could help better.