The scriptural core is short. Brahma prepares a sacrifice at Pushkar and Savitri, his wife, has not come when the auspicious hour arrives. Since the rite needs the wife's presence, he marries Gayatri and proceeds. When Savitri appears she curses him: he will be worshipped at Pushkar and nowhere else. The Padma Purana is the text Wikipedia names for this.
The temple's own telling begins earlier and ends more generously. Brahma slays Vajranabha with his lotus, and where the petals fall three lakes appear, which is how the place gets its name. At the sacrifice Gayatri is a local Gurjar girl. Savitri's anger falls not only on Brahma but on Indra, Vishnu, Agni and the officiating priests, each with a curse of his own; Gayatri then softens every curse so that Brahma will still be worshipped at Pushkar, and the others with him. The temple's sanctum admits only ascetics; householders offer through the priests.
What is different here:
Adds the demon, the three lakes, Gayatri's Gurjar birth, the curses on Indra, Vishnu, Agni and the priests, and Gayatri's mitigation.
Above the town, on Ratnagiri hill, Savitri has her own temple, reached by a climb or a ropeway. The present building is twentieth-century but its image is said locally to be from the seventh century. The story is told from her side: the wronged wife who withdrew to the hill and still looks down on the husband's temple.
What is different here:
Savitri's viewpoint; the hill temple as her retreat.
Guides tell it in one line: Savitri cursed Brahma never to be worshipped anywhere on earth but Pushkar, which is why, they add, this is the only Brahma temple. The claim of uniqueness and of two thousand years on the site is part of the telling, not of the record.
What is different here:
Compressed to the curse and the 'only temple' claim, which the record contradicts.