Probably didn't have all 350K at your bid price and other bids that came before yours at the same price would be filled first. Also, MM's have no requirements to fill a buy order even if they have shares available. It's all a matter liquidity and the MM's, something that will drive you crazy trying to make sense of. IMO
Dolly if you dont have L2 Quotes I woulld suggest getting it as you can see how many shares are available on the bid and ask.I hub usually will let you try it out for free-no credit card etc. needed to see if you like it.