score:2
Shikantaza in original usage means ~'only sit', and the term was introduced into fairly standard usage by Dogen Daishi c.1250AD. This is in the context of Original Traditional Authentic Soto Zen, where the term is fairly similar to zazen, which means ~'sit & contemplate' etc, and so, within context, the two terms authentically mean about the same thing: sasaru means to sit/squat, & is pronounced 'za' in that sort of word construction, and zen means ~think/contemplate. In the term shikantaza, the 'zen' part is inferred from context, and shiken in this context means ~only.
Traditionally, in Soto Zen, shikantaza & zazen aren't directly about concentrating on breathing or on the nose or on relaxing, etc, and shikantaza more explicitly indicates that with the 'shi' meaning ~'only' part. So maybe the Asker was participating in something that was was similar but might have differences in meaning and of what's meant by the terms zen & shikantaza!
This answer is from the context of The Traditional Soto Zen instructed c.1250AD by Dogen Daishi. There may be other places that use the term shikantaza and the term zazen differently. Nice interesting question.
Upvote:3
To sit in zazen is to sit facing emptiness. M H's answer is absolutely correct, but like most things in Zen there is more to the story once your practice deepens. Relaxation and concentration on a focal point have their place, but really what zazen is after is the arousal of mushin or "no-mind". In early Zen, and later in Soto, they sat in pi-kuan or wall gazing. You'd literally just sit facing a wall. No fancy techniques, no mantras, kasinas, or even the breath. Just you, your cushion, and a surface staring back at you. As you advanced in your sitting, little by little, things began to fall away. (In fact, if you don't allow them to, you will drive yourself batty doing this practice.) As that is happening, concurrently, you'll also begin to internalize that blank wall. This happens through no effort of your own. As you let go of you, emptiness is revealed. Eventually you become the blankness - mushin - itself. The wall becomes secondary if not entirely ancillary.
So don't worry about your thoughts, don't worry about the tip of your nose, and certainly don't worry about spontaneity. Just sit and don't move. Stare at the wall and see what happens.