According to the plot, the guy plays a dating simulator and angers God, and he transfers him to the game (then it turns out that he created a world similar to this game) and infuses the guy into the body of the girl of the main character. To return home, he must complete the game.
I remember that the manga is in black and white. I can't say for sure; maybe about 30 chapters?
Maybe Tadashi Ore wa Heroine Toshite? It seems to be about a boy who is transferred to a dating sim, but as the main girl, instead of the male protagonist:
After the manufacturing company of R-18 dating sims undergoes dissolution, an obsessed 30-year-old virgin visits a deserted shrine and requests to be sent to the world of their masterpiece, Kokorone Heartful. Although his wish is granted, the god mistakenly turns him into the heroine instead of the protagonist. Ordinarily the romancing choices are left to the protagonist. However, unless he completes the game as the heroine, he will be forced to remain in Kokorone Heartful as a woman forever.
