I think you can close that gap by continuing to work the problem. Try tightening all of your stitches a bit at a time. You may need to tighten ones that are quite some distance away if the panels don't overlap and bend as they should. Don't be afraid to break some stitches and replace them. Also don't be afraid to drill some additional stitch holes where needed.

+1 on everything Birch2 says, along with strategically loosening some stitches, to let the wood move, and re-tightening them when the wood is secured in its new place.

If that was my boat, I'd try slightly loosening the stitches between the sides and bottom at the middle and raising the center of the bottom. I'm thinking that will make the 2 sections come closer at the bow.

Good luck,

Laszlo

... and if Birch2 & Laszlo's suggestions don't bring you closer, enlist another pair of hands to help move those panel edges into compliance then tighten the stitches, or add new ones.

Sometimes the force of tightening one stitch at a time just isn't enough - it being applied at such a concentrated point along a panel's edge - to make things move as you'd like them to. There's no shame in using what's available (tools, muscles) to get things into a shape that then will be secured by means of those stitches.

(In exchanges I've had with Dillon M. as my Waterlust comes together he allowed that 1/8" can be 'close enough' with stitch'n'glue, but if with extra effort that 1/8" can be brought down to 0? I have no issues with taking that path!)

Good tips from all the masters above.  I would add that how and where the boat is supported changes the shape a bit.  After you lossen some of the stitches, I would flip the boat over and support it near the bow.  This will allow the boat to sag into a bit more rocker which will help your gap.  In addition to the, try pulling the top of the top panels together with some tape between the fwd BH and the bow.  This will give the top panels a little less rocker which also should help.  This is a fiddly part of the build and you have to keep working at it until you get it right.   

With our PMD, we found that, yes, bottom down with the ends propped up helped things come together, along with progressively tightening all around with a bit of wriggling back and forth of the entire shape once things got close to coming together.  Sometimes the plank edges at the overlaps will stick a little in spots, and bit of this in the middle can manifest itself as a bigger gap farther out.  Extra hands can be a big help at this point.

....Michael

   Having preached perfection last night, I'd like to come back to endorsing moderation! I looked at my own Shearwater Sport this morning and see that I have a gap of 1/16th inch in the same place. I have it filled with peanut butter epoxy and sanded it fair. I never notice it.

   Thanks everyone - good suggeztions I need to noodle on next steps