It is very common to get nervous just before starting your Camino. This isn't necessarily a good reason to change your plans at the last moment.
At this time of year, every year, the forum and other Camino web sites get lots of panicked posts from first timers about how busy it is around St. Jean through Pamplona.
Above this you have received good advice from a variety of experienced pilgrims.
At these times I often post about my own experiences of leaving St. Jean on the 15th May 2019, still one of the single busiest days for this stretch. I only had a reservation in St. Jean for the first night and I always had a bed.
Of course, I might have somehow been lucky because I certainly encountered other people who were panicking about not getting a bed and because it was my first time it was hard not to join the panic conversation.
One thing has changed since 2019 and that is the number of beds that were held back for walk-in pilgrims at Roncesvalles. They used to hold back two thirds of their beds but now they only hold back around a quarter.
Roncesvalles is definitely a pinch point. You have excellent advice on how to manage this and the options are:
1 Reserve a bed in Roncesvalles
2 Take two days to cross the Pyrenees so that you arrive in Roncesvalles early enough to get a non-reservable bed. I would aim to be there around 11 am although I don't think that they are open then.
3 Walk on past Roncesvalles to find a bed. Generally easier if you have taken two days to cross the Pyrenees.
4 Share a taxi with other pilgrims from Roncesvalles to the nearest empty bed. A good way to meet new people and make friends and memories. Then taxi back to Roncesvalles in the morning.
Lastly, as a couple of wise people have already mentioned, aim to stay at Zabaldika. A donativo albergue that does not accept reservations and a definite highlight of my first Camino.
If you are resilient and have a problem solving approach then you will be fine and you will have a fantastic and memorable Camino.
Remember, we are not walking solo across some great, untracked desert, we are walking in France and Spain, first world countries with mobile phones, public transport and wayside cafes and bars
. This is part of the magic. A real challenge within a very safe environment.
Buen camino!