if your CT scan was clear, it might just one of those little lumps we all get from time to time.
But if you are really worried - it would probably be a good idea to call your BC nurse tomorrow morning and discuss this with her.
I remember from reading another post on your initial diagnosis, that you did not mention, whether it is suspected that it might have spread to the nodes in your arm....?
As you are due for chemo next week, even IF - this one has escaped from being noticed - the chemo is being given to kill cancerous cells.
For reference where nodes are in our heads -
I hope this helps a little bit - I am so sorry that you are struggling so much. You had an awful lot of information to take in in a very short space of time. It is absolutely understandable that you are worried, as it appears you have had hardly any time to digest everything. Make as much use, as you can, of your BC nurse - they are great in explaining what is happening and they have access to all of the results, too.
Have you joined the June chemotherapy thread yet? You might find a lot of support there to help you through this challenging time. In case you have not and to make it easier - here is the link -