Cutting teeth takes about a week. That's part of the reason he's so sketchy right now.
To help him calm down, allow only dim lighting into the tank. If you put things like towels on the edges of the tank for a few days, that will help him to not damage himself by smashing into the edge of the tank while he's settling.
Being shy and flighty is the nature of all tiny silver fish. Right now, he is food for larger fish and his temperament reflects that. When he gets up to 6-8 inches, he'll calm down tremendously. He's likely to be a very difficult fish to keep for the next month or three.