Outstanding use of common sense. Seriously. And in my both personal and professional opinion it's something that isn't used NEARLY often enough in our sport by some people. I sincerely commend you for making the tough decison.
The P-38 is a fantastic dive and often one of the easier deep dives in S. California. But that being said, it is in an area conditions can change, making it challenging. Couple that with your discomfort and the way the mind plays tricks upon us when we are unsure of ourselves and you are just asking for a myriad of problems.
If you've not done so, take a deep specialty class. Honestly, this doesn't so much "certify" you to dive deep but will do a good job of familarizing you with the ins-&-outs associated with visiting this and my other sites like it safely. After that get some time in practicing with a buddy you can trust. You don't have to practice at 120ft. Simulate it on your normal, every day dives through out the region. Get in the habit of safety stops. Get in the habit of putting a time limit on your dive and sticking to it and all the other tips and limitations you'll be introduced to. Then work your way deeper incrementally so as to get used to how fast your cylinder is consumed at deeper depths and such. Take note of the length of time it takes you to safely ascend. Learn to factor all that into your personal dive planning.
But most importantly, keep listening to that little voice in the back of your head. It sounds like it will steer you the right course and keep you diving for many years!