Well done, the first solo QXC is another one of those milestones in doing your PPL - but if you think the buzz from that is good then you'll be over the moon for your qualifying QXC!
Re intercom boxes, I've always found them to be a bit of a mystery, a classic case of too few controls with far too much functionality ( to use a sad IT phrase). Its normally quite easy to find the correct combination of toggled swithces to achieve the desired result but it is a bit hit and miss and I can imagine it would be unsettling on your first QXC! I think there is a case for better briefing in this area, and possibly to have it examined in the theory papers.
Again well done - you made some mistakes, nothing fatal, no one hurt, probably no laws broken
, and you've cleary taken some learnings away from the experience.