Diaper rash / scratches?? Help please.

My son (17 months) must have scratched his penis somehow. The last time I changed his diaper wasn’t long ago and he was perfectly fine.

After playing for a while, he started screeching. I checked his diaper and I feel like a horrible human being for not seeing the scratch. His whole groin is red, and he had not only peed but recently pooped so all of that got into his cut!

It looked very swollen and irritated, I cleaned it well even though he screamed and I used a very good diaper cream.

Has this ever happened to anyone else or am I the only idiot 😭 I am sitting in the bathroom crying my eyes out.