Hi, thanks for your query.
As you have mentioned that worst part of burn was on your shoulders, it seems that these red bumps are due to sun burn reaction.
For this you may use a moderate potency steroid cream twice a day for a week to ten days.
Avoid sun exposure as much as possible.
If there is no sign of improvement after applying steroid cream or the rashes increase then you may have to consult a dermatologist
to rule out other cause of bumps like contact dermatitis
or fungal infection
Hope this helps you.