Is a sin or expiation required from one who intended to perform Hajj and went to observe its rituals, but was unable to do so because the campaign organizer refused his inclusion, despite the presence of intention and waiting for a mahram?

If you have not entered into a state of ihram for Hajj, then there is nothing upon you. However, if you have entered into ihram, then you are still in your state of ihram, and it is not permissible to exit it except by completing Hajj, or by exiting ihram due to being prevented (ihsar) along with offering a sacrifice (hady), or by exiting ihram with an excuse if you stipulated that (when entering ihram). If you missed the standing at Arafat, then you must exit ihram by performing Umrah.

You must avoid the prohibitions of ihram. For the prohibitions of destruction that you committed (such as shaving hair, clipping nails, and hunting), you are required to offer a fidyah (expiation). As for the prohibitions of comfort (such as sexual intercourse, using perfume, covering the face, and wearing gloves), there is no fidyah for them due to ignorance.

After that, you may either wait for the next Hajj to perform it, or you may exit ihram now by performing Umrah. If you are unable to return to Makkah, then your ruling is that of one who is prevented (muhsar), so you should offer a sacrifice (hady) and exit ihram. In the coming year, you will be required to make up that Hajj.