You can do any of the following:
1. Hover your mouse over the body until you see 3 dots next to your cursor (...) then select the body and there should be a small box pop up called Quick Pick with a listing of features and geometry. See if Solid Body is in there somewhere. If it is, you've successfully sewn the sheets into a solid. If not, then you need to delete the Sew feature, find where the gap is at, repair it and recreate the Sew. See #3 for some tips on checking for a successful Sew into a solid.
2. Set your Preselection Type to Solid and hover your mouse over the body - if it highlights, you have a solid.
3. Delete your Sew feature and pay close attention to your Cue/Status line as well as the graphical feedback as you recreate the Sew. Any unjoined edges will highlight in red after you press OK/Apply. The Cue/Status line will flash something to the effect of "Solid Body created" very quickly.
Tim Flater
NX Designer
NX 8.0.3.4
Win7 Pro x64 SP1
Intel Xeon 2.53 GHz 6GB RAM
NVIDIA Quadro 4000 2GB