A 3.86 is not a bad grade by any means. Yes you have a low grade in Spanish but you have a high GPA. You realize you don’t need a 4.0 to get into some good schools. These posts are starting to annoy me with the I have a terrible GPA then have a 3.8 which is far from terrible.
With 3 AP classes, your max possible UC GPA is about a 4.0 assuming straight A’s in spring semester. A sub-4.0 GPA wouldn’t be competitive for UCSD, UCD, UCSB, or UCI Engineering, but you should get into the lower UCs (UCSC, UCR, and UCM), most of the CSUs, and possibly Cal Poly SLO.
One C will not “make or break” your chances, but since you are aiming for a competitive major at competitive UC’s, it will be slightly harder. Finish up your Junior year and see where you stand. I agree that your GPA is not terrible, but you may have to lower your expectations. There are so many good schools beyond the few you have listed, where you could do well and excel in Engineering. Keep up the hard work and Good Luck.