If you want to keep these gaps and make them another color, just create a new layer and put it behind the layer that your label is on, then fill it with the color of your choice. If your design is locked and named "Background layer", just right click the layer and "duplicate layer". Then put the colored layer behind this duplicated layer.
If you want to get rid of the gaps, then just use the crop tool. You can adjust the box before finally cropping your image, so you can fine tune the crop area before pressing enter and cropping the image, which will reduce the canvas size and display just the area you specified using the crop tool.
I hope that helps! Post a pic of your label when you're finished
To post a label just use a website like http://imageshack.us/
Upload your label, then copy the "Hotlink for Forums" code and paste it into your post
You can delete the [ URL] [/ URL] tags if you don't want any intrusive hotlinks.
Also use the "Save As" options in Photoshop to resize your image accordingly so you can post it on a forum