Hi
Before I give help, just want to say this is not my product, but I do now use it and so happy to offer a response.
For the admin preview, it will only work if all the correct options are there, because it is those that create your preview on the admin side. It may be that somehow your database has become corrupted, so if you have kept a back up I would first restore your wordpress to a copy where everything was working.
One thing I can see from your preview window is very small, and your icons tiny, is this how you meant it to be, or is this also not working out properly? From what I can see this is not how the original default file would look so I am assuming you also made some changes to the skin (class-vpc-default-skin.php)?
In your case unless you have literally hundreds of designs, I would start afresh, re-install the plugin and return to the original default layout, it should work fine for the type of product you are displaying. Also, since this plugin is responsive so will work on a mobile, you should consider making your images bigger – they will shrink automatically for mobile phones and it means that desktop users can really see the detail on your designs.
If this is not really something you can personally do, given the price you are looking for your product, I would look at places like fiver (for images) or upworks (for software development) to help with getting the best looking product configurator for you.
I am working on my own website, so here is a preview of what this software can do, it does have its limitations, but you can make it look really cool! So happy configuring.
https://www.pinkequine.com/pinknew/configurator/configure/521/ (this is a test site so you cant actually buy at the moment!)
p.s I haven’t done the responsive CSS on the changes I did make to this, but if you make the page smaller to mobile size you can see how the default css changes the layout and the image is put below the options.