Framebuffer clipping anything drawn 'off screen' - c++

Question

I recently implemented a zoom-in/zoom-out function in my simple 2D engine and experienced some terrible seams between adjacent textures, as shown here:
http://oi59.tinypic.com/anmxyf.jpg
It doesn't look that bad but it was definitely annoying when it was constantly blinking at you when moving around.
I decided to change it so a very large portion of the game (as much as the player is allowed to zoom out) is instead drawn on a framebuffer, then I print the framebuffer and when zooming in or out it instead increases/decreases the framebuffer texture size, as to avoid the seams.
At first I decided to draw 5 times as much as is visible to the player at default zoom, so I made a framebuffer object with a texture 5 times as big, then draw to it.
Here is the initialization of the framebuffer object:
glGenFramebuffers(1, &main_framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, main_framebuffer);
glClearColor(0.f, 0.f, 0.f, 1.f);
glClear(GL_COLOR_BUFFER_BIT);
glGenTextures(1, &main_ColorBuffer);
glBindTexture(GL_TEXTURE_2D, main_ColorBuffer);
glTexImage2D(
GL_TEXTURE_2D, 0, GL_RGBA, SCREEN_BUFFER_WIDTH, SCREEN_BUFFER_HEIGHT, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL
);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glFramebufferTexture2D(
GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, main_ColorBuffer, 0
);
Where SCREEN_BUFFER_WIDTH and SCREEN_BUFFER_HEIGHT is set as five times as big as the default screen size. I then draw my world as I would normally do (where I could zoom out as much as I wanted and everything was fine, except the seams).
The issue is that only 1024 x 768 (being the default screen size) is drawn to the framebuffer. This is how I activate, draw to the framebuffer, then draw the framebuffer:
glBindFramebuffer(GL_FRAMEBUFFER, main_framebuffer);
glClearColor(0.0, 0.0, 0.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
draw_blocks(); //draws all the blocks in the correct screen y and x position
glBindFramebuffer(GL_FRAMEBUFFER, 0);
glBindTexture(GL_TEXTURE_2D, main_ColorBuffer);
draw_quad(shift_y*ratio, shift_x*ratio, SCREEN_BUFFER_WIDTH*ratio, SCREEN_BUFFER_HEIGHT*ratio);
glBindTexture(GL_TEXTURE_2D, 0);
Where ratio is a float I use for zooming in and out and shift_y and shift_x I use to shift the framebuffer texture around to get a better feel for how things are going.
By zooming out and shifting the framebuffer a bit I get this:
http://oi61.tinypic.com/34zlpip.jpg
it only draws a small portion of the screen (which exactly fits the screen if I don't zoom out).
In contrast, this is what it looks like if I zoom all the way out (and then some) before using a framebuffer and instead drawing straight to the screen:
http://oi61.tinypic.com/21akbit.jpg (the empty parts are just chunks that haven't been loaded as the player isn't supposed to be able to zoom out this much).
I'm truly stumped here, I've tried changing the viewport before drawing but this does just about nothing.
I'd also like to note that I'm pretty confident the actual framebuffer texture object actually is five times as large as what's being drawn to it, because if I don't stretch it in my draw_quad function by instead giving it the same width and height as the screen, I get this:
http://oi62.tinypic.com/4triiu.jpg
The width and height of the framebuffer is now the same as the width and height of the screen, yet there's only graphics in a fraction of it, which is the small portion that's actually being drawn to.
Anyone have any clue? If more portions of code are needed I'm happy to oblige but the entire thing is far too much.