Yes to that. Don't feel badly. I was so over-eager, I didn't want the teachers' LOR's folded into thirds, so bought S-2 flat 8x11.5" envelopes; then had him affix the wrong postage - short by a few cents because I didn't know the post office uses size, not weight, to determine postage.
Greatly impressive. Fortunately nobody's anything had left the GC's office yet. I immediately phoned it into the GC who added some penny-postage, and son ran to add to the petty cash supply of the GC.