Nonsense! Shallow, superficial people judge others by "first impressions". It is an indication of intellectual laziness (and very likely impairment), of an unwillingness and possible inability to think deeply, analyze, and make informed decisions. A woman who makes a snap judgment of you based on a "first impression" is hardly worth bothering with.
In general, you, as a shy person, need not lose much sleep over what
sort of "first impression" you make on people. It is quite sufficient
to come across as 'neutral', relatively nondescript, incapable of
being categorized and placed into a convenient slot. You are a quiet
and reserved person, enigmatic, profound and unfathomable, marvelous
in your complexity, and you need wear no mask, no false flamboyance
to intrigue others. If your style, your manner, your inner radiance
provokes others to think, to pause, reflect and wonder, you will
make an unforgettable impression.
Wisdom dictates holding back the most important parts of one's self at first contact, in favor of a gradual and orderly getting acquainted period. Getting to know someone, truly know them, is a slow and sometimes messy affair, full of risks and potential missteps, and only a fool would attempt to short-circuit the process by relying on a 'first impression'. There is much more to a person than can be taken in at a single glance, and, as is generally the case, "what you see is not what you get".
How much more powerful than making a good 'first impression' is the
satisfaction of shattering people's preconceived notions about you, of
literally being reborn in their eyes as a novelty, a bright and shining
unknown. The dawning awareness, the dazed bewilderment of their awakening
as they realize they had not really known you at all... and that they
need you to enrich their all too ordinary lives, this more than
makes up for being ignored and passed over at first sight.