At that rate, 5 hours, figure you did about 40 runs, so about 240 drops.
52/80 of Baal's drops are equipment items capable of being unique, so about 156 of those.
Baal has a base chance of dropping a unique version of an item of about 1/16. With 350 MF, that improves to about 1/6.5. So, your 156 equipment drops would expect to yield about 24 unique quality drops.
About 60% of the base items in Diablo have unique versions defined for them. For example, if you get a Targe drop there is no unique one so even if it qualifies to be be unique the game can't give you one. So you lose uniques through that. That brings us down to around 14 or 15 uniques expected (assuming none of your numbers are exaggerated).
Binomial distribution, p = 15/240 = 0.0625, n = 240. q = 0.9375.
Mean = np = 15, SD = sqrt(npq) = 3.75. n= 240 is a large enough sample to approximate it to a normal distribution. 3 uniques is 3.2 SDs outside the mean, which has odds of roughly 0.0007, or 1/14000 of happening.
Geez mate, that's some bad luck.