Creating a Flat Surface on a Curved Surface?


I need to put wholes in them to make an attachable spoiler thing. Its a curved surface and I cannot make holes in it, so I opened it

Bad thing is, it wont make a face anymore, it just makes empty squared and stuff, I clicked on the sies and everything, it wont make faces and I downloaded make face plugin, still wont work. Can someone help me? If you want to get hands on and stuff, email me for the file cause I cant send it becasue it reaches max capacity.

Plus even after you guys help me fix it, I am printing it from a 3d-printer and Its is hollow inside, my teacher told me it will print not hollow, like it will print filled in but how is it supossed to recongize that I need a hole here to attach my spoilers? Ask me if you need any more explaning, this is for my science fair and I need this done asap for expiriemenation and everything…please help me…and email me for anything,

This is duplicate of above making surface error

You can use either Vertex Tools or Artisan to make a flat surface on a mesh