The sooner you get the colonoscopy the better, then you will almost certainly learn that it is IBS and made worse by worrying. Of course, when you are worrying aout the symptoms, the worry make them worse, which makes you worry more, which . . etc etc.
However, your GP is very thorough, and wants to rule out the small chance that it could be a tumour - that is a good thing, and you wouldn't really want miss the chance of finding out early and getting it fixed, would you?
Stop Googling, you have found out too much for this moment when you are stressed about the whole thing. Concentrate on what you are eating, and look out for anything that seems to increase yor problems - knowing that could be very useful once the IBS is confirmed.
You could spend the time while you wait for the test (and the results!) in keeping a food diary and a symptom diary, and comparing them. You might find some simple combination of ingredients makes things much worse or much better. Start by only eating very bland things (boring!!!) which are said to not exacerbate IBS, then day by day add more exciting ingredfients and note the effect.
In a couple of weeks, you may find that you can just about diagnose IBS yourself, and also which things you are best to avoid!