Do not double up on pills. Just keep on taking them one at a time starting today. There is no magic to starting it on a Sunday.Starting on a Monday or Tuesday is just as good. If you really want to keep to a Sunday start, skip the last two inactive pill of this pack on the last Sunday and start the next pack that Sunday (so only take 5 of the inactive pills).
Remember that you may still be fertile for a week after starting, so also use condoms. Condoms are anyways a good idea if you are not in a long term relationship.