The white residue (haze if applied properly, very thin) are the ingredients used as a carrier for the active ingredients. When the Sure Step dries, the active ingredients are deposited into and onto the gelcoat and the carrier remains as the white haze that you see. It needs to be wiped away or buffed off prior to applying the 2nd coat and after the 2nd coat to bring out the beautiful shine that has been hiding on your deck.
From your description, I believe that you will have two problems. First if water gets into the residue before the active ingredients are allowed to bond to the gelcoat, it will prevent this from happening and since this has occurred and left for two weeks, it will be difficult to remove by wiping or buffing. The second problem is that you will probably have dirt and pollution on the deck that needs to be stripped off before reapplying the Sure Step.
A good analogy would be rain on wet paint and then leaving it for two weeks. Painting over will only make the mess worse, resulting in a poor finish and possibly adhesion problems. You need to strip it and start over.
In your case, you shouldn't need to rewash with Boat Clean Plus unless there is a lot of airborne pollution where you keep your boat (near an airport or in an industrialized area). Just scrub the deck well with Boat Scrub and reapply the Sure Step, being sure to wipe away or buff the haze off after each coat. I suggest working in a small area at a time, 3 or 4 sq. ft. It's easier to remove the haze if it is not allowed to dry too much and if you put on thin rather than thick coats. I like to use a jeweler’s buffing wheel on the end of an 18 volt drill instead of rubbing with towels and brushes. It's a fast and easy way to remove the haze and it also brings out the shine better.