First, let's run the numbers:

9 x 11 x 7 = 693 / 5 (total exchange every 5 minutes) = 138.6
x1.5 for each 90 elbow = 69.3 x 2 = 138.6
x1.3 for the carbon filter = 41.6
+10% for each foot of duct including lights. I'm going to guess 10 feet of duct work = 138.6
Each hood adds resistance. I suggest we use a x 1.2 for each hood = 27.7 x 4 = 110.8

Now we add it all up:

138.6
138.6
41.6
138.6
110.8
-------------
568.2 CFM

You should be fine with that 746 CFM fan. You said your grow room is sealed. Does that mean there are no passive intake vents? If that is the case then that is likely your problem. You need to add them. The rule of thumb is that the intake should be 1.5 the exhaust so with an 8" exhaust you will want 12" of intake.

If you are truly running sealed grow then I suggest you add a vent for your lights such that the lights vent in a closed loop whereby the vent goes from external into a duct through your lights and back out. No need for carbon filter in that loop. My read is that you are not really doing a sealed grow room in which case cut the vents so that your fan can do it's work. It doesn't matter if it is pulling warm air. Anything will be cooler than 95 degrees.