I think you will probably find that whatever you get your weight down to at its lowest, you will gain about 4lb almost immediately as its your glycogen store and the associated fluid restoring itself. Its a battle I have been dealing with myself since getting to my target. Once your weight levels up again, it will most likely settle down, but its means (for me anyway) that I need to go a few lbs lower than target and then let it settle upwards somewhere.
I understand your panic though, its something i go through every day wondering what the hells happening with my weight as im pretty terrified that it will just keep going up. Sensibly I know it wont as long as im eating properly and not going over the top.
How much did you lose in all to get to target? There is going to be an adjustment period while your body sorts itself out at your new low weight, and while thats going on, it will want to regain at least some of the lost weight. Maintenance is a path filled with pitfalls.
You absolutely do need to go back to class this week and get weighed, time of day will affect the actual figure too, and it may not be as bad as you think. But even if it is, then now is the time to deal with it, dont put off going back to class. You are not losing face by showing a gain, you are in maintenance and this is just part of the journey to that end.
To me, it does seem a bit mad to straight away whack an extra 20 points a day onto your food just because you hit target. I would go for a much slower increase, and monitor whats happening weight wise. Maybe add an extra point a day until you find what levels you out. That way it will take 3 weeks to get up to that extra 20 points a day and you will have a better idea of how much extra you can really eat.