Scared of bigger breeds and then own one?

I posted earlier today re: puppy buyers remorse - my husband and I bought a puppy yesterday and made the mistake of buying a 3 month old shepherd/lab/pitbull mix EVEN though I am truly terrified of bigger dogs (bad incident with a pit bull that happed a few years back -the pit bull was an old roomate of my husbands dog, I was left alone with that dog one day while visiting, I tried to take her outside where she literally dragged me around the entire yard even though I was pulling with all my might - I had NO IDEA how strong that dog was, then it started growling and ripped her leash in two when we were finally getting in the door, where I proceeded to lock myself in the bathroom as she bounced off the living room walls and snarled/barked,and I waited there crying until someone came home!) basically the dog was alone all the time and had a lot of pent up frustration but it was scary. Anyways, now not only do I look at this puppy who is already at the max size I'm comfortable with, with a large knot in my stomach knowing how big/strong this dog will get (I'm only 5'3 110lbs), I think about the fact that and I don't want to come home to a frustrated large dog every day (has to be crated during the day 8-5 and at night since not potty trained), and my poor cat has already fallen into depression (like me I guess).... I told my husband the best thing to do is take the puppy back when she's still small, instead of waiting until she's bigger and I feel uncomfortable, however he is bonded now and has the notion to just give it some time... But how will he feel if I don't overcome the big dog fear and he gets REALLY bonded? I don't want to be scared of the dog a year from now, decide I can't do it anymore, and have my husband hate forever for getting rid of his best friend... Any advice? Is it best to just return puppy now or wait and see if I can overcome my big dog fear?