Why Leave Some of the Lump??

I have just had loads of tests and finally an operation to remove a lump under general anasetic, I noticed as its healing that the lump is still there, I went to the drs who said yes she can still feel a lump (I suppose I should be grateful that at last I had a woman dr!!) she said they could have just left some in, why?? Id already had a needle biopsy. I hope I dont offend anyone on here by asking if it seems petty but my circulation is bad and they couldnt get a vein so I was gassed for the op and it was really horrible. My mum died quite young form BC so I appreciate the thoroughness of the tests ect but I dont understand why Im assuing I was last that day, I held them up due to the gassing and they rushed.