Yes, you can add cocoa butter to the chocolate while it is tempering. I have a chocolate chemistry book, I suggest you get one as well and start reading why these things are happening to your chocolate.
Never fill the molds all the way with the filling so you have room for the chocolate bottom.
you can freeze the mold for a few min to help it set up, but too long and the chocolate is shot, so stick to taking your time until you have enough practice.
find a chocolate maker and trail or stage for a while (work for free to gain education).
Read the manual several more times so you know your machine cold.
Did you test the Tempered chocolate before placing it in your molds? Always test until you can tell by feel (like when you're 90!)
to test the chocolate once the machine tells you the chocolate is in temper, take a metal spatula and dip in the chocolate, wipe off one side and let the knife set out for 10 min. If the chocolate sets up without flaw, you are good to go. If the chocolate is spotty, splochy, has stripes or does not set up, try again.
Do not waste your time using bad chocolate.
Happy Trails.