Then I used my belt sander to try and sand down to my line.
It took FOREVER! So then I cut part with my miter saw, but that only would cut about twelve inches into my 1X2. Then I took a hacksaw and went at what was left.
At least two hours after starting I had the wood for the left gap ready. And I was dreading the next day when I would have to do it all over again on the right side. But, the next day I realized I was being a dope. This doesn't have to be filled in with one continuous piece of wood. So I cut my 1X2 into twelve inch sections, marked the angels I needed to cut and used my miter saw to get it all done in less than half the time it had taken me the day before.. I'll need a little extra putty to cover up where the wood meets, but I plan on using a ton anyway, so what's a little more? I also bought a couple of wooden shims to fill in the much narrower areas.
Then, today, I had to actually attach all of this wood. I bought a small container of liquid nails and quickly realized that I didn't have the right angle to smear it onto the sides of the bookshelf. So, I got creative and gooped the glue onto the handle of a fan and spread it with that.
I maneuvered the wood into place and shot a couple of brads to hold it in place.
It doesn't look perfect, but hopefully the putty will smooth everything out and hide the imperfections.
Here's how it looked before:
And here's how it looks now:
I'll let you know how the puttying goes!