I have booked every night of a three week trip and I am now wondering what that costs me

The rule that resolves most of this: book what is genuinely scarce, and leave open what is not.

Scarcity is the whole criterion, and it varies enormously by destination and season rather than by how organised you are.

Book in advance:

• Flights, obviously
• Anything with limited daily capacity - a permit, a timed entry, a popular restaurant, a specific tour
• Long-distance trains where reservations sell out or the price rises steeply
• Accommodation in a place with genuinely little of it - small islands, a festival, a national park gateway, anywhere in high season
• The first two nights, always, because arriving tired and hunting is miserable
• The last night before an early flight

Leave open:

• Accommodation in cities of any size, outside peak
• Regional transport that runs frequently
• Most days of most itineraries

So your three weeks probably contains three or four things that had to be booked and about fifteen nights that did not.

What that buys you is the thing you are worried about losing: staying an extra night somewhere good, leaving somewhere early, following a recommendation. On a three week trip that flexibility is usually the difference between a good trip and a memorable one.

The structure I use on longer trips: fix the ends, loosen the middle.

First two nights booked, last two nights booked, and the flights that bracket the whole thing. Everything between is booked a few days ahead as I go.

Why the ends specifically: arrival is when you are most tired and least capable, and departure is when a mistake is most expensive. The middle is when you are acclimatised and can handle a change of plan.

Booking a few days ahead rather than on the day is the practical middle. You get the choice and the prices without committing three weeks out, and you avoid the genuinely stressful version where you are looking for a room at eight in the evening.

Two things that make this work in practice:

Have a rough shape, not a schedule. These are the four places, roughly this order, roughly this long. That is enough to keep you moving and loose enough to change.

Book refundable where the price difference is small. Often it is a few percent, and it converts a fixed plan into an option. Where it is a large difference, that is usually a signal the place is in demand and should be booked.

On your current trip: check the cancellation terms on the middle nights. You may be more flexible than you think.

Worth stressing that this is mostly a question about where and when, not about how adventurous somebody is. The people improvising successfully are usually travelling somewhere with slack in it.

What pushes you toward booking everything:

• High season anywhere popular
• Small places with few beds
• School holidays, festivals, public holidays: check the local calendar, not your own
• Anywhere with a single road in and one bus a day
• Travelling as a group, since two beds are much harder than one
• Anywhere you need an address for a visa or an entry form

What makes improvising easy:

• Shoulder or low season
• Cities
• Regions with a dense network of trains or buses
• Travelling alone
• Somewhere with a well-developed accommodation market

So the honest answer for your trip depends on facts you have and I do not. If it is somewhere busy in August, booking it all was correct and the flexibility was never really available. If it is a shoulder-season trip through mid-sized towns, you have bought certainty you did not need.

Either way it is not a mistake: a fully booked trip is a completely legitimate way to travel, and plenty of people prefer knowing. The thing to avoid is doing it by default and then feeling trapped, which is what your question is actually about.