I've not got direct experience of this, but didn't want to read and run. I have read a lot of other people's posts, including quite a few from people with the same question as you.
You said you had "colposcopy treatment" - do you mean that the colposcopy (which is the bit where they have a look at your cervix) showed clear changes, so they did the LLETZ treatment there and then? Because if so, quite a few ladies have been called back to the hospital a bit like you have, and then been told that they need another bit of LLETZ treatment. They want to see a certain amount of space around the bad cells they took out, i.e. they should have got the bad bits plus a bit around the edges to be sure. If they haven't achieved the "clear margins" that they want, they may be getting you in to explain that they need to take a bit more.
There are quite a few posts on here from people who have had this situation, so being called back to the hospital doesn't necessary mean that the worst news of all awaits you there.
Fingers crossed that it is all OK for you