Surfing Waves

I'm a beginner surfer and my surfboard is a gun (medium sized board made for big waves). I realize that this is not the ideal board for a beginner but it is all I have now.
I have been using the board for a while, started in breaking waves and now am going further out for larger waves, where I do better. My question is this. Are there special considerations I need to know for using a gun? The main thing I've begun to be aware of is that I really have to get my front foot up as far as I can on my popup and then push down hard or I fall off backward. I'm still having a hard time getting up though and also struggle with sitting on the board.
Does anyone have advice for me?

Brandon, Hi and welcome, mate post a picture of the board and dimensions of both you ( weight and height) and the board, because gunliness ( new word there folks) is next to shapeliness. The shape of the board determines whether it is a gun or not!
BTW you are doing well if you are figuring out the changes you need to make to your pop up and stance
keep at it.
The advice is be forward in your stance and your sitting too far back and the board will eject like a cork from between or under your legs.
Beginning days

My board is 7'6 feet long 21 inches wide and two inches thick on the rails. It's thicker along the center line probably about three inches thick there. As far as it's shape goes it comes to a sharp point in front and a rounded point in back. It has three fins.
I am 5'9 and 175 lbs.
Most of the waves in my area are knee to chest high.

That's not a gun.
Guns are thin and narrow for their length (Jaffa will explain it much better than me). What you've got sounds like a pointy mini-mal, or a funboard (everyone hates that description, but funboard just means halfway between a mini-mal and a shortboard).

But what you've said is still true - you'll need to make sure your weight is a little forward for the drop, and you'll need to weight the back for the turn.