Nope, you are starting in the wrong place, a begginer does not start at the lineup.
Go out about to waist to chest high surf and wait for a nice moving whitewash come come your way. When it gets close to you throw yourself towads the shore with enough momentum to get the board going, then practice your popups. Do it over and over until you stand up more often than fall. If you can stand up 5 times in a row then you are ready for step two.
This will result in 3 things: 1) you will develop a smooth popup for when you can catch waves and 2) it will give you a better sence of balance on the board and 3) you will catch waves and fun right away. Yes you will look like a kook, cause you are one, so get your popup right first. Once you have your popup down you will get more comfortable with your board, which will help your paddling.
As to learning on a shortboard,the board is fine, it's easier to learn on a longboard, but many (even me) learned on shorter boards.
