Ooohh, now I understand better. I thought the point was the multi-color effect of the gem would make the number stand out for them. But it's more the shape of the gem, to make users think "gem".
In that case, at least based on the extremely limited info I have, I might wonder if a diamond shape might say "gem" more than the rectangle shape you showed. A shape like the quick sketch I just made (attached). Oh....or maybe a little pile of different gems?? (Sorry, once I start thinking about peoples' projects, sometimes I can't corral the brainstorming.)
Good job with the Pen/Bezier tool! It's not too hard, right? Here's how you can join the left and right sides. The end nodes don't necessarily need to be on top of each other, but they could be. It depends on how much precision you need. Anyway, using the Node tool, and with both paths already selected, drag a little selection box around the end nodes of both paths. Then click Join Selected Nodes button, on the control bar
Do that for the bottom ends and also for the top ends. Then you have a nice closed path.
Depending on how things went with the Pen tool, it's possible the left and right sides that you drew weren't connected themselves. You might have noticed that when either the Pen tool or Node tool is enabled, and the path you drew is selected, there is a tiny box at each end of the path. If you want to continue that path, without having to come back later and join the nodes, you can place the mouse inside that tiny box. It will turn red when the mouse is in the right place. Then click once. Now you are ready to continue that same path, and you won't need to come back later to join the new path to the old one.
Sorry for all the words. It takes 50 times more words to describe how to use the Pen tool, than the actual steps you need to take with the tool.