Try not to worry. Easier said than done, I know. The waiting game is horrible but ultimately worrying doesn't help in the end.
The fact it's described as a 'polyp', however big, is better news than finding a tumour, because there's a good chance it isn't cancer.
Now, about the size. Bigger is more concerning, but how much? I did a little research and one study said this:
No cancer was found in polyps < 5 mm in size. However, the cancer incidence was... 42/973 (4.30%) in polyps > 30 mm in size.
So while your 3cm polyp is more worrying than the smaller one which is almost certainly nothing, there's more than a 95% chance that what you have is not cancer. I wish I could tell you it was 100%, but for now, assume good news until you hear otherwise.
All the best.