I realized that I did not pressure can my tomato sauce long enough. The lids sealed.. Can I put them back in the canner like that to finish ? It has been several days  
The sealing of the lid means that no new bacteria or micro-organisms can get into the food, but if you didn't complete the full pressure cooking process you may not have killed everything that already existed in the jar. If you realized this the same day that you originally canned, you would be fine to re-process (break the seal, dump everything out, wash/sterilize, and try again); but once a few days have gone past you have to assume that the food in the cans has continually been exposed to whatever still may be in there, and the food is going to spoil. For safety reasons it would be best to dispose of the batch and start fresh. 