I intentionally left a 8cm gap between laminate and a wall because there was an uneven wood beam in the concrete along the wall. I had the same problem in another room and I just put laminate over the bump and seems OK, so I think leaving the gap was a mistake.
Is there any way to fill that gap so that it ends up being same level as the rest of the floor. Ideally without a transition piece that sticks out of the floor (like a t mold).
For example, one solution would be to glue many 8cm short laminate planks and effectively lengthen the existing pieces. But I'm afraid it won't look nice and moreover some of the ends of the existing pieces are not perfectly straight as they were cut.
Best Answer
If your floors have their seams lined-up like the diagram (very wrong), it looks quite bad already so adding a bunch of scraps on the end won't hurt. The best solution is to literally start over & use as many of the old pieces in the manufacturer's instructions followed new & proper floors...that have at least 3 rows laid as a dry fit so you don't have any pieces shorter than 30cm.
Each row of planks has its butt seams offset from the next row & at least the same for a third row before you repeat. One main reason for this is exactly your situation here. Be careful & conscious with your measurements & cut 1 board at a time...do I leave the line, cut-out the line or split the line.
With varied lengths meeting the wall you can custom cut & even scribe each piece's end for a flawless fit or common very minor manufacturer's gap. Also, any ridges, popped nail heads, splintered subfloor faces, heavy paint or glue deposits, etc. should all be flattened, leveled, sanded, chiseled & removed prior to installing the new floor.