Did I make a mistake on my booking?

I think you would be okay, but maybe someone here might have more details. I know last year when I booked with KLM, I added my middle name in there, as it is on my passport, but they just connected my middle name to my first name on the ticket. So it was basically one long name. I was a little worried about it, but read here that this is typical of European tickets because they don't usually have or use a middle name.

And of course, the name on the ticket did not really match my passport, but no one ever said a word, so I assume that it would not be an issue.

I always book with just first and last name although my passport shows my middle name. It has never been an issue.

Not exactly applicable, but I had a problem with TSA precheck several years ago, on a domestic flight, because I did not have my middle name on the airplane ticket. Because my middle name was on the TSA precheck paperwork, the airline insisted that I put my middle name on the airline ticket.

Of course, this would only (possibly) apply to your TSA precheck status, but just mentioning this because sometimes airlines get finicky.

Just a crazy story, but it's also important to supply a middle name if you have two people with the same first and last name in your group. We flew once with my father and my niece--they had the same first and last name, but different middle names. American Airlines decided that we had purchased two tickets for the same person! It was easy to sort out, but gave us a few moments of panic, for sure!

Well thankfully our ticket from SEA to AMS was done separately, so my name is correct on that. Delta has messed up beyond belief, and sold us a ticket to Stuttgart but then said they can't get us there. So we are just tossing that portion, and changed plans and will fly to Vienna upon landing at AMS. So no TSA involved for that leg. I am gad to hear that it shouldn't be a big deal. I am just always so careful with this stuff, but it was bad timing with pain meds and booking, lol.

My passport has my middle name. Only one airline, Delta, puts in my middle name. None of the others. Never had a problem with TSA Pre-Check or Global Entry.

Icelandair and Alaska both put my middle name on my tickets, as does Delta. I will just wait and see how it goes.

United runs my first name and middle name together as one long first name. I was told several years ago that’s their system’s limitations.
If you’re worried, call KLM to update. You’ll have your passport as proof of your name.

I just did a booking up to the point of entering the passenger info and KLM has only a first and last name box.

There is this advisory on their website

For travel to or via United States, all passengers need to provide various personal details (such as date of birth) to the authorities. After booking your flight, please make sure to enter these details in My Trip

When you go to the "My Trip" is there a way to enter a middle name?

Without actually buying a ticket, I do not see anywhere to include a middle name.

Here is a recent anecdote. 3 weeks ago, friends called me for advice. They were taking a Viking river cruise in Europe and purchased their airline tickets through Viking. They gave their names as first name, middle initial, last name. Two weeks before departure, Viking informed that they had to charge them $350 per person to reissue the airline tickets because their passports contained their middle names. My advice: "Viking is full of s***, just go with the tickets you have." Result: They made it to Europe without issue.

Joe--I think that explains it. I probably followed the directions at the time and then just never thought about it again. I did try to edit my name and there is no way to do it. I will just go with it and we will get there one way or another.