Well, it depends on how big your space is, but I would recommend an Endless Summer or Blushing Bride Hydrangea. You could underplant it (them) with a few spring bulbs and add even more interest in early spring.

Love hydrageas but have never had one that was fragrant, are those fragrant? Plus it cant get bigger than 30x30 inches.
Jill

Both of those hydrangeas will be very simple to keep within the size you specify. You can trim them anytime, because they bloom on new AND old wood, and bloom continually. Fragrance? I have never noticed any on these two, though many hydrangeas are very lightly fragrant. I know of no truly fragrant plant that has that long a bloom time. Most fragrant plants bloom for only a short time. Roses would be the exception, but I know of none that are that small AND fragrant, plus, your sunlight might be inadequate. Sorry.

I find the Antique Rose Emporium website very helpful. You can probably find a small rose with fragrance, repeat or continous bloom and shade tolerant. What about nicotinia, an annual? Not sure if it needs more sun.

I googled "fragrant annual" and also came up with heliotrope, but by the name, it might want more sun.
Also I checked Antique Rose Emporium. If you go to order online, or maybe rose list there, you can click on small shrubs, and you can see the heights, whether they repeat, and fragrance. You can also search for shade tolerant roses. I quickly saw a few that should meet your requirements: Cecile Brunner, Clotilde Soupert, Gruss an Aachen.

I guess it will have to be a annual to get fragrance all summer. Can't have roses at the backstep because I have a 4 yr and I would worry she would fall in to them. Trying to find a good pic of heliotrope. Found a plant the other day that smelled heavenly called wallflower but if my memory serves me correct it will only bloom this year and not the next plus I think it needs full sun.
Jill

I am not trying to be a wet blanket here, but heliotrope will not last any longer in our heat than pansies, if that long, and nicotiana, in my experience shuts down in summer heat and looks ratty long before the season is over.

Daisy-flowered gardenia-- long bloom, nice shiny leaves, & won't mind the mid day break in the sunshine. These are slow growers & don't get as large as regular gardenias. You could tuck a pot of star jasmine in the area for additional fraagrance!