So...I'm a doofus and made my 1st mistake. My original design had to change because the board size I wanted wasn't available, but I forgot to update the plan. I mixed up what length I was supposed to use and made the internal measurements within the raised border too small, meaning instead of having a 20" x 33" space for the track plan, it is now 19.5" x 32.5". The overall measurements of the layout are still 21" x 34".
Since I already spent money on the lumber and time cutting and sanding it, I will go ahead and use what I have. Luckily, the only thing I need to modify in my design is not being able to have a raised edge to protect the trains. My plan is to raise the underlying support boards by 1/4" which will allow the foam board to be level with the outer frame. I will have to come up with another way to create a protective border because the track will end up resting right where the raised edge would begin, and trains would come in contact with it.
My grandfather always said, don't just measure twice and cut once, triple check and cut once. I measured three times alright, just used the wrong measurements haha. Oh well!