Surfing Waves

Hi, I've recently purchased my first board (secondhand) it's 6ft 6 took it out for the first time yesterday to test it out and was my first time out since lessons. Managed to catch a few waves but as yet can't seem to get myself to pop up and just get to my knees. Gonna get out obviously again and practice but I'm just a little concerned whether the board may be slightly too small or whether I just need to work on my stability as was a little wobbly. I'm 5ft 3. Any advice would be much appreciated.

what kind of board were you riding before? I am 6ft 2 and can pop up on a board that is 6ft 2 so I don't think it's too small