I decided to take AP physics my senior year. If I earn a D in that class for 1st semester will it affect my csu application?
Why wouldn’t it? It is part of your transcripts.
If accepted to a CSU, you need to have no D’s or F’s your Senior year. I would contact your GC and also any schools that you have applied. Most schools are willing to work you and may just watch you until your final year end grade. Do not let this go and hope for the best. Be proactive.