I was wondering, do I have to do problem set 0? I already have prior programming experience, and I'm hoping to get an Honor Code certificate, but Scratch seems a bit ridiculous to me (without wanting to offend anyone, cause I'm sure that people new to programming may find it useful).
Unfortunately, yes! Per the course syllabus page
Students who earn a satisfactory grade (60% or higher) on every one of nine problem sets and on a final project will receive an honor code certificate from HarvardX as a downloadable, printable PDF.
However, I was once in a similar situation since I also had a prior programming experience, but my advice to you is that you try to "use" this prior experience and create something unique comparing to other projects and regardless of that this is the first pset in the course.