If you want the fiberglass tape to not show you have to take care of it before you put the covering on. What you need to do is first fill the weave off the fiberglass tape with either resin or wood filler and sand it smooth. To hide the fiberglass tape completely you need to use resin or wood filler and spread it out from the edge of the fiberglass tape out for about 2"-3", then you need to sand this down and feather it in so that there is a smooth slope up to the tape. Depending on the wing you may have to go out further than 3", but you get the idea.

Hope this helps

Ken