Hello,

I do not think that you will be needing a gap certificate for just getting admission and then leaving it after a few days. Nowadays, taking a one  year gap is quite normal. In fact if you think you can get a better opportunity then it is fine. Moreover, it would not affect your placements if that is your worry. If you take a gap of 2-3 years or more then you need to make a gap affidavit.

Now affidavit is a legal document so you have to get a lawyer who would help you to get a stamp paper in which your reasons will be mentioned.

Lastly, your character certificate is to be given by your school. In case they do not provide it then try to get a letter by your principal and that would work .

Hope it helps.

Good luck.