That's a good route, but I also have another suggestion, which is slightly different.
Day 1: Shimla to Narkanda Start your journey from Shimla and drive towards Narkanda. The distance between Shimla and Narkanda is around 60 km and can take approximately 2 hours. You can stop by at Kufri to enjoy the scenic beauty and snow-capped mountains. You can also visit the Mahasu Peak for a panoramic view of the surrounding mountains. Once you reach Narkanda, you can explore the town and stay overnight at a hotel or homestay.
Day 2: Narkanda to Sangla On day 2, you will drive from Narkanda to Sangla, which is around 120 km and can take approximately 5 hours. The route takes you through the picturesque Kinnaur Valley, with beautiful views of the Satluj river and the Kinnaur Kailash range. You can stop by at Rampur to visit the Padam Palace and explore the local market. Once you reach Sangla, you can visit the Kamru Fort and the Sangla Valley. You can stay overnight at a hotel or homestay in Sangla.
Day 3: Sangla to Chitkul On day 3, you will drive from Sangla to Chitkul, which is around 26 km and can take approximately 1 hour. Chitkul is a small village located near the India-China border and is famous for its beautiful landscapes and traditional architecture. You can visit the Chitkul village, the Mathi temple, and take a walk along the Baspa river. You can also go for a trek to the nearby mountains. You can stay overnight at a homestay in Chitkul.
Day 4: Chitkul to Shimla On the last day of your trip, you will drive back to Shimla from Chitkul. The distance between Chitkul and Shimla is around 230 km and can take approximately 8 hours. You can stop by at Kalpa to visit the Kinnaur Kailash range and explore the local market. Once you reach Shimla, you can explore the town and visit the famous Mall Road. You can stay overnight at a hotel in Shimla.
Which ever route you take, enjoy the road trip.