Paris Day Trip

What do you think of going on a trip to Paris alone? Is it safe? The return trip will cost less 100 quid but I have to take the first trip to Paris as it is the cheapest and return at 7ish PM that night. I have been to Paris before but I haven't seen the city properly. I went to the Eiffel Tower, did the boat ride and tour around the city on a bus on my first time. I still have so much to see, Sacred Heart, Louvre(I haven't been inside) and NotreDame de Paris. I need more convincing! Hahaha!