From longboard to shortboard

Hi All
I have been longboarding for about two years, and have bought a fish 6´3 and i can´t get up standing on the board.
I am used to a 9´6 but have tried 8´2 which also worked out fine for me.
Should I sell the 6´3 fish and go for something in between a 8´2 and 6´3 or should I just keep up and learn eventually?
Im 6´2 high and weigh about 165. I usually ride in small waves no more than head heigh.
Hope you can help me
Chris
I have been longboarding for about two years, and have bought a fish 6´3 and i can´t get up standing on the board.
I am used to a 9´6 but have tried 8´2 which also worked out fine for me.
Should I sell the 6´3 fish and go for something in between a 8´2 and 6´3 or should I just keep up and learn eventually?
Im 6´2 high and weigh about 165. I usually ride in small waves no more than head heigh.
Hope you can help me
Chris