Sorry for your frustrations. I can certainly understand how you feel. I fear multi-part masking, as previous attempts have been failures. Lately I've been thinking about using my Silhouette cutter to make uniform width strips, because I can't seem to line things up worth a damn using just my eyes or a ruler.
And dropping? The closer I get to the end, the more I seem to drop a kit. Sometimes it seems the line between getting it done and chucking it into the bin is very narrow.
You've done well.