This happens all the time with making candles in molds (as opposed to dipping them). It is because as the wax hardens, the molecules are settling down and hence taking up less space. This is the opposite of the ice/water relationship which is rare in the world of liquids and solids (water turning to ice actually EXPANDS due to crystal structure). But I digress. You can add more wax and it should adhere just fine. The hot wax will melt and fuse with the solid wax where they contact. Depending on the size of the mold, you may have to backfill a few times. One way around this is to simply trim the candle with a hot knife. Hope this helps.

cheersblessings

Hey Michelle. As said, the wax sinks in the midle as it cools and the outside cools faster. What I do is add more hot wax before the middle starts to harden. This way you don't get a 'seam line' showing.

Thank you guiys that really does help!

Craft Lab did a show yesterday on candles.............they would take bits of old/other candles and then torch them on to new candles. you should check it out.