sometimes it takes the temp to rise back up as it has to heat all the cold air inside as it surcomes all the hotair once the bator is open, also it could take some time for the thermometer to catch up to they can be picky at times but being at 97 wont hurt it that much if any at all for that...
yes toilet rools are fine you can switch to egg cartons any time before day 18 or even day 18 but the earlier the better, and the whole raising one side of the egg carton isnt really a good method as it puts some eggs higher up then the other half which means they will be in diffrent temps also...