Is there a limit to the size of my nether portal?
I made this nether portal. Is it too big, or am I doing something wrong. I barely got it in one screenshot. 
This is far too big.
The portal dimensions you can use are between the following (for the obsidian frame):
Minimum: 4x5
Maximum: 23x23
It also doesn't need to have corners.
The Nether Portal that you are building is too big as prior to the 1.7 update, only Portals sized 21x21 (I think so!) are allowed to be lit up and be used. So, make it smaller.