Passthrough related issues are still in Beta, so if you need help with that in the future, you will want to post questions on the Passthrough Beta thread. 
Looking at your design placement…move it over to the left side of the screen. Work off of the left side, not the right. (And 18.75" might be just a hair too wide for it, try scaling it down to 18.5" wide or a little less…I had trouble with reads on really wide prints that extended all the way out to the right.)
I know it’s a long read, but there are tips in that thread that tell how to get the best results with the Passthrough…be sure to at least skim through it, and you will pick them up easily. (And save a couple of days waiting.)