If your flute is an open hole flute, this means you will have to be precise when closing keys because you have to both close the correct key and make sure the pad of your finger is centered over the hole to prevent air leaks. If a key is not completely sealed, you won't get the note you expect.

If your flute is an open-hole model and you are having difficulties you might consider purchasing a set of plugs. A temporary solution is to use small squares of masking tape, or some other easily removable tape (not cellophane or "scotch" tape), to cover the holes, though this is not ideal.