I got severe blistering sunburn on my shoulders from being in very high uv at high elevation, will i just be at much greater risk of developing skin cancer on my shoulders or am i at much greater risk for developing it in unexposed areas too?

Even without sunburn, exposed skin increases risk for skin cancer, but blistering sunburn is more predisposing. Unexposed skin is less likely to have tendency to later development of skin cancer but often those areas were exposed in the past. Genetic factors & immune suppression are other features that play a role in later skin cancers. Blistering sunburns are the worst!!