I just started surfing 3 days ago and I'll apologize ahead of time if I'm asking anything that makes you guys roll your eyes

Saturday I was at San Onofre and I was out for about 5 hours with a long board and had a really good first time experience, caught a few waves and thought my endurance was pretty good. Tweaked my knee and ankle on the rocks so I skipped going out Sunday.
Today (tuesday) I went out to El Porto with a shortboard which I also have and completely different story. I was done after an hour. The waters were pretty rough and beat me up pretty good, caught 0 waves.

So to the question; where would you guys recommend I go for calmer waters in the LA/long beach area that don't have a lot of people for me to get in the way of where I can just paddle/balance and build up my muscles endurance?

I know some of you are are already thinking I shouldn't have been on a shortboard so soon off but I wanted to see myself where I stand and where I need to improve from the start and that's the goal I'm working towards.

thanks for checking my post,