No reverse

I have a 1995 Toyota Camry that has been sitting in my driveway for three months since I went away to college. I came back to visit, put in a new battery and drove it about 250 miles. It drove perfectly fine, and reversed out of my driveway, but when I parked after my long drive, it will no longer go into reverse, though it will go into drive fine. I’m thinking that it might have something to do with the transmission, but even so, would it be safe to drive back the 250 miles?