Timing Belt Replacement/Tapping Noise

I got a timing belt replacement kit that has the timing belt, the timing belt pulley tensioner with spring, water pump, and pulley. I did top dead center, everything lined up and then I started the vehicle for about 10seconds to observe and the timing belt was walking off the camshaft pulley and then I checked over everything and that everything was tightened to spec and did a top dead center check again and now there is a tapping noise coming from what sounds like the valves. The car has been in the inclined position for about 7 days. It has been in great condition, the vehicle belonged to my father who gave it to me as a gift. He always would take it to the dealer for maintenance and they would use a BG Motor oil Additive. Any idea what the tapping could be? I've added some oil to it because it was low, maybe due to the incline. Any help/advice would be greatly appreciated.