Good baby shower intentions gone bad...

I'd love to hear if someone else has had a similar experience of good intentions gone horribly wrong...misery loves company I suppose?

I have been in my current department for about 3 years now.  A co-worker offered to throw me a baby shower.  The company I work for has 6,000+ employees, so I think the ettiquette is a bit different than when I worked for smaller companies (and all employees were invited to a shower).  My old department consists of 15 people only a handful of whom I keep in touch with (and by that I mean casual emails a couple of times a year). 

I ran into my former boss (from 3 years prior) and during the conversation she invited herself to my shower (she had caught wind of it).  Ok, fine.  I also decided to invite two additional people from that department who I keep in touch with.  I asked the boss if she thought I should invite the whole department; I explained that I didn't want to come across as greedy, and didn't want to be rude to my current co-worker that was buying all the food, decorations, etc. She never replied to my message.

A few days after my shower the old department came to my office with some baby gifts...and a lot of agitation at the boss.  I was so stunned by the gifts that I honestly didn't connect all the dots before they left.  Essentitally, old boss invited the entire deparmtent the day of the shower, and never told me she invited them. 

I feel terrible, mostly for people getting their feelings hurt (they are very nice people), and b/c they are mad at the boss when really it's my fault for not inviting them upfront.