Yours is a common mistake made by many DIYers. One is supposed to undercut the door casing and jamb to allow the flooring to be installed UNDER those vertical obstructions. You will now need to remove that board next to the door and undercut the jamb and casing. Then cut a new board to install that slides under the casing and jamb.
From
HARDWOOD INSTALLER DIYer tips:
Quote:
Cutting The Door Casings
Quality installations need proper attention to preparation and detail. What to do around the door casings is oftenPreparation of hardwood floors. Undercutting door trim asked. They should be trimmed to the same height as the flooring so the hardwood will slide underneath providing a clean professional appearance. Professionals rely on power jamb saws that cost $200-300. If you have a few casings to cut a hand saw will work just fine. Using a scrap piece of wood, lay it directly on the concrete cutting the casing with the hand saw flat to the scrap wood.
If you have more than a dozen door casings to trim, renting a power jamb saw is an option but hard to locate. Many flooring tools I've mentioned can also be obtained online.