Is the measurements in inches or centimeters or what? For a single chin you want at least a 3ft x 2ft x 2ft cage, or 91cm x 60cm x 60 cm, so either way the cage sounds big enough. Also the image attachments don't work on the forum, you'll need to upload the pics onto a photo share site then link it.
I'm not sure what kind of hay burgess is or what kind of herbs are mixed in, but at 3 months you should be primarily feeding alfalfa hay. You can also feed some timothy too, but they need the extra calcium from alfalfa for growing. You don't really want herbal hay just yet either, you want the chin to eat the hay not the herbal treats mixed into it. You also don't want to be using degu pellets, they are not formulated for chinchillas. You want a chinchilla pellet food, one that is pellets only, no extra junk food in it. I'm not sure what is available in the UK but a couple good quality chinchilla foods brands that I'm pretty sure you can get there are Mazuri and Oxbow (the Essentials Deluxe not the new garden one). Supreme Petfoods Science Selective Chinchilla is another I've seen people mention that is in the UK, that looks ok as well.