just to wish you good luck tomorrow and to maybe take someone with you for support. It's pretty scary when you're not sure what to expect and I don't think the letters are always helpful.
Just had a quick look on this site and it describes CGIN as this:
If your cervical screening result shows abnormal cells you may be asked to attend a colposcopy appointment. Remember testing positive for CIN or CGIN means that you have abnormal cervical cells that may lead to cancer if untreated, but CIN and CGIN are not in themselves cancerous. Treatment for abnormal cellular changes is usually very successful.
If you're being called into colposcopy it's likely they are wanting to have a better look and might take a biopsy Which may sting a little but will give more accurate results. I was called in with very little explanation and thought it was just a routine check up and they ended up doing something called a Loop excision under local anaesthetic. Essentially removing any abnormal cells to prevent further changes or spreading. Again it stings a little but fairly minor.
It was then a few weeks wait for the results which is probably the most stressful bit so keep yourself busy.
Its a good thing they are getting you in quickly and hopefully they can give you more information tomorrow.