Rising action means that the challenges faced by your protagonist begin by being fairly easy to overcome, but as the story progresses, those challenges escalate and become more dramatic, and more difficult and taxing for her.
In your plot, therefore, you’re moving always towards a climax. For sure, you’re always building towards the final - story climax, but each scene will also have its own mini-climax. This means that there’s lots going on for the reader - lots of questions being raised, and lots of reward for her in the form of some of the questions answered.
Will they successfully gain entrance to the castle?
Yes, they did.
Will they successfully steal the jewel from the castle?
No, they didn’t, they’re discovered in the attempt.
Will they manage to make their escape?
Yes, they did.
What will they do next to get the jewel?
It could be argued that the purpose of every story is to show the protagonist's journey from incompetence to competence, from ignorance to knowledge, from fear to courage and so on, depending on the theme of the story. In other words, every story is integrally about the character's growth, and the plot is actually only a device to both cause, and illustrate, that growth.
So, the original small challenge only required small skills and determination to solve. It didn’t stretch the protagonist too much. But because of the rising action, the next one is harder, and stretches her more.
The story explores/reports how she finds, learns, or unearths the resources within herself (as well as external sources as needed) to solve the challenge in some way.
Or, maybe she doesn’t solve the challenge, but that teaches her and helps her grow, and better prepares her for the next challenge.
In successfully overcoming each challenge (even if that overcoming consists of successfully escaping), the character is growing in strength (physical, emotional, mental and maybe even spiritual), which will better prepare her for the final, greatest challenge, at the story climax.
The principle of rising action will be easier to explain with examples. Let’s talk about the first Shrek film.
The main dramatic question is whether he’ll get his swamp back. But in order to do that he has to meet several challenges.
The first, which is easy-peasy, and indeed, comic, is when he just roars at the soldiers and they all run away.
The second challenge is harder, obeying the rule of rising action - he has to beat all the soldiers at Farquar’s palace.
The third challenge is more difficult again (i.e., more rising action) - he has to beat the dragon.
There are then subplots, i.e. his growing love for Fiona, but they all lead up to the final story climax in the church, when the dragon breaks in and Farquar is beaten.
Do you see how this works? Rising action all the way.
At the end of each scene, make sure that the reader knows there’s more to do. The characters mightn’t do it immediately (it’s important for pacing to have breaks between action scenes), but they (the characters and hence the readers) certainly know that it will come.
You can leave that knowledge percolating as you explore some other element of the story - a subplot maybe. Or perhaps the characters are talking about the next stage, or planning for it.
Rising action keeps the tension and the suspense strong, which keeps the reader reading - which is always the aim.
You know the way they say that a politician’s only job is to be re-elected, and the road-building and industry-supporting and hospital-resourcing are all only the means to that end? Well, a writer’s real job is to keep the reader reading, and the plot and excitement and tension and dramatic question and so on - are all just a means to that end!
I’m quite serious, and it’ll help your writing in a big way if you keep this in mind. As you write each section, ask yourself if it’ll keep the reader reading. Your reader is always just one sentence from putting your book down and never picking it up again. Your job is to make sure that doesn’t happen.