Getting GIMP to recognize text outside old borders

I've been trying to create an image showing mitoxantrone (a chemo drug) intercalating DNA, as part of this I've had to combine two structures -- a DNA strand with the molecule found therein and the molecule up-close and in detail at the side of it. The DNA strand had to be rotated using Paint.NET (as GIMP had similar problems to what it does now, as it hides anything outside the original canvas when rotating) as the software I used to create it made it difficult to create the image portrait. Then I expanded the canvas so as to allow me to add this additional image (of the molecule up-close) into it by copy-pasting but for some reason any image outside the original canvas (of the DNA strand) is hidden. How do I overcome this problem? Here is a screenshot showing what I mean.