How long was the car ride? Are you in a location that has a lot of Covid cases?
And do you live with your mom?
I feel like that was a pretty short car ride, but you live in a place where there have been a lot of Covid cases and your friends were not masked. If you want to be cautious, wear your mask at home for two weeks to protect your mom.
You very well might want to get tested. I'm not sure how you're going to wear a mask at home all the time, that's where you eat and wash etc. The proper answer is if you really thought you were exposed to covid you need to quarantine yourself for 14 days, not just wear a mask, as nobody wears a mask all the time at home. Now, if you have access to a quick results test that is an accurate test, you would know more. I gather you're probably fairly young, and the sad reality is that right now that's where most of the infection is circulating because young people are not following CDC recommendations, as your two car mates did not do. There is also no way to know if they have covid or not, as most younger people are asymptomatic but can still spread the disease. Now, would I personally do these things? I don't know. I'm not young, so I'm never in that kind of situation. I'm married and my wife is pretty much the only person I've been close to for any length of time since this thing started without wearing a mask. 15 minutes in a car isn't the longest or most intimate contact you can have with someone, so I don't know what the risk really is, but just going by the guidance, if you wanted to do what was the perfect thing to do, you would quarantine until you had a couple of negative tests, and most of us don't really have access to that kind of testing. For the most part, it's unlikely this will end up infecting anyone -- it's not like you were with them for a long time maskless. I think it's between you and your Mom. I also would say that, although California is the hardest hit state in the Union even if you lived in a state with very few cases you could not be sure because those states also don't test as much as California. We know a lot more about California than, say, South Dakota, which has few people but no restrictions on behavior and very little testing encouraged. So who would really know? This is the world in which we live right now. I'm guessing if I were in your shoes, I'd just go on with my life. Young people are a lot more active and social than older ones especially right now, so the risk is much more prevalent. But if I were king, I'd shut down the whole country and start over until the disease count was driven way down, and we didn't do that. Peace.