Does touching the penis to the anus constitute sodomy in itself, or is it one of its preliminaries, bearing in mind that it occurred in a state of remorse and repentance?

First, praise Allah for the blessing of repentance.

Second, be sincere in your repentance by abandoning the sin, regretting it, and resolving not to return to it. Show Allah devotion and turning towards Him, and weep over your sin.

Third, this act is forbidden, repulsive, a gateway to indecency, an aggression, and a pleasure taken in what Allah has not permitted. However, it is not the act of sodomy that incurs the prescribed punishment (hadd).