You’re doing great! Having a B or two (or three, or four) on your transcript will not affect anything. You have a normal fluctuation of grades, and no specific trend in any way. At this rate, you will still have a GPA of over 3.9, and be in an excellent position for anywhere.
AP Physics 1 is notoriously difficult, so you are hardly the only smart kid who has difficulty with it.
There is nothing at all for you to stress about. Again, you are doing great.