Shortboard Pop up Help

Hey guys,
So for the last 2 months I been surfing a 6'3 shortboard but I've been having a few problems with popping up. Every time I go to pop up on the board my feet end up being to close together making me fall straight off. Also when popping up on green waves I catch the wave but I have trouble getting up on the board until I get to the bottom of the wave as I feel like I am going to nose dive. Where and when I surf the waves can be around anywhere from 3 to 6ft.
The 6'3 is the only board I have right now as a mate sold it cheap to me and I can't afford to buy a fun board or something with more volume at the moment meaning I can't learn in whitewater
I understand that learning on shortboard is crazy hard but I guess a few tips would help (I have searched the web quite a bit too) . I have skateboarded for 7 years but surfing to me is way different.
Cheers.
So for the last 2 months I been surfing a 6'3 shortboard but I've been having a few problems with popping up. Every time I go to pop up on the board my feet end up being to close together making me fall straight off. Also when popping up on green waves I catch the wave but I have trouble getting up on the board until I get to the bottom of the wave as I feel like I am going to nose dive. Where and when I surf the waves can be around anywhere from 3 to 6ft.
The 6'3 is the only board I have right now as a mate sold it cheap to me and I can't afford to buy a fun board or something with more volume at the moment meaning I can't learn in whitewater

Cheers.