Seeing the merged image you have in your signature right now, it's not a bad start, but it could certainly use some improvement. Maybe it's because of my OCD, but I can easily see that the banners are not perfectly aligned, with overlap and gaps between many of them. Not to mention, the way they're arranged leaves a lot of black space that could be filled in more easily to make the combined image a little smaller.
I can see there are 13 banners to arrange, and I think the best arrangement would be 3x4 (or 4x3, depending on which way you want it to be) with the one leftover going in the middle of the bottom row.
Since you seem to be a little new to this, I would suggest asking someone to help you out with making the proper corrections to your image.