Baby rash on arm

So I feel utterly terrible like a horrible (first time) mother. My week old had newborn photos taken yesterday and I wrapped him in a little cheesecloth-like swaddle. Well almost instantly i noticed a rash on his arm coming up, and took it off immediately. I then realized I forgot to wash it. I literally washed every item he will ever wear, in Dreft newborn detergent, except for this photoshoot swaddle I forgot! Thankfully the rash is just on both his little arms and nowhere else.. But what can I do? We bathed him, and I put breastmilk on it three times now in hope of that helping but it’s only a smidge better. I’m wondering can I put desitin or aquaphor on it? He has a dr appt tomorrow thankfully but I wish there was something I could do today. Tia