Yes you are close!! If you have all day sunday, I'd recommend going up into san diego. imperial beach is really cool, and it's nothing but beaches and oceans there! on the mexican side, rosarito is supposed to be nice, however it's a half hour cab ride that would be expensive. I really wouldn't recommend driving in mexico. you have to get extra insurance and it's a little crazy and easy to get lost. i'm hoping you fly into san diego and could rent a car for the day there. all of san diego is right on the water. driving up 101 is great also. lots of cool little beach/surf towns. just grab a map at the rental place and go explore! ocean beach is really fun to hang on the beach.
also, god bless TJ, but it is a border town.... don't be expecting cancun.... you can take a cab from the hotel to "Revolucion" which is a touristy street that is pretty fun. It's a $5 ride. Lots of street vendors, fun restaurants, and probably the best place to go if you decide to stay in TJ. There is not much right around the hotel.... some apartments, a mcdonalds, some businesses... some restaurants....
hope this all helps! go to SD!