Buy yourself some thinset,it looks like this is piece is not glass underneath.Take your piece of glass and put a dab of thin set on it with a craft stick,then smoosh it or build it up to the heith that is the same as your other pieces.I do this all the time.good Luck.You can buy a little thing of premixed tile adhesive and it will do the same thing if you don't want a big bag of thinset.

Wouldn't work for this project since there's the heat of a candle involved, but for projects that don't require the glass to be totally transparent, you can use pieces of thin plastic like the lid for a butter tub. Like Annie said, thinset would probably be the best option for this.

HTH,
Pat

Thanks ladies. I'll have to try the premixed tile adhesive cause I'd never use up a big bag of thinset.

Be Safe, Rach

I like the pre-mixed adhesive for interior projects. It has instant stickability. You can get thinset in 10-lb boxes at the box stores, and I'll bet even smaller quantities at a tile store. My tile store sells it by the lb.