How to fill this gap?

[Tom]

Hi all - we have a mezzanine area that we need to get carpeted and unfortunately the chipboard flooring boards don't go quite to the edge (see pic). There's about a 35mm gap x 5m, which is just too wide to be covered by the carpet gripper strip. I'm unsure what to fill this with, the timber just visible is the wall plate and there are a few gaps that extend in to the ceiling void, so anything liquid will flow into these. What would you suggest? I don't have any more of the woodchip to use unfortunately. 

Thanks 

[Oz07]

A 2x1 behind the skirting board. Otherwise cut flooring back and fit a bigger fillet. How far back is the joist?

[Tom]

Thanks @Oz07, there wont be a skirting board along this side, and the joists run perpendicular to the gap.

I could run a circular saw down the gap and cut off the "tongue" of the chipboard flooring, then use a 35mmx22mm strip of wood to fill I guess.