A common problem for beginner guitarists is getting chords to ring out nicely. You followed the instructions, you have your fingers in the right place, the guitar is in tune but when you strum the chord it just doesn't sound right. If you were to pick each note and listen carefully you might find some of the the notes sound dead or muffled. Getting it right comes down to the positioning of your fret hand.
It's all about practice as your fingers need to be positioned "just so": not too far from the frets and not directly on top, don't press too lightly or too hard. Finally make sure that your fingers aren't fouling other strings, this can happen if you are not using the tips of your fingers to fret. The link below has a good article about fret hand positioning for beginners.