Can't 'create solid' when trying to knit surfaces

Hi,

I am working on a SolidWorks project using the 2017/18 version to create a thermal thermometer. I used surfacing to create the form I have however when I try to knit the part there are gaps that I don't know how to heal. If anyone is experienced in this area and has

some advice that would be greatly appreciated.

SolidworksSurfacing