Don't worry about it. Sometimes it would be almost rude NOT to notice after a woman has gone to a lot of effort to make herself look great. It doesn't have to have any sexual connotations at all. Although happily married I quite openly comment positively on women's looks, clothing and even hairdo's. They invariably take it in the way it was meant, as a compliment.

But in any case you did nothing untoward and there is no apology necessary.