Whether you do it yourself or send it out is immaterial except the board house can mate top and bottom a lot better than you can. There are easy techniques I have used for many years. The first is to make sure that the Datum or Origin of the board has a common marker in the same place on top and bottom. If you use 2 alignment targets at diagonal corners and outside of the art work then align the film by the targets and clamp the film in the contact frame, expose one side and without moving the registration from top to bottom flip it and expose the other side, develop, etch, clean and drill. The process is very easy but you NEED to create a method to align both sides of the film on the sensitized area and off board so they can be seen and used. This is the way to get the holes to line up. Try it with a small PCB as practice, You will soon become used to the process and it will get a lot better. I haven't made a 2 sided board at home in 40 years but that was the way I did it... Right out of a book on home-made PCB's... Worked great.
Doc