Help on alto saxophone? I cant get the middle octave B natural?

I just got an alto saxaphone today and started playing with the standard of excelence book. I have had a little expierience with tenor sax and could play most of the notes fine (size 2 1/2 reed). the alto i got is a rental but is in great condition and im using a size 2 reed. i have had lots of musical expirience, i play the flute and piccolo, but i dont know why i cant play the middle b natural note. maybe im putting in too much air? every time i try it goes up an octave. any help is greatly apriciated! thanks! and nothing is wrong with the instrument, the music store fixed it up and checked it earlier this week.