Firstly, if you have been poorly then you shouldn't even be worrying about your Syns. The main thing that you focus on is you and becoming better.
Secondly, if you have a gain, you have a gain. There's nothing you can do now - you can't un-eat those Syns (unfortunately!) All I can suggest is that, if you're feeling better now, get back into the plan to limit the damage. Also, drinking lots of fluids may help.
Thirdly, and most importantly, please please please go to group. It doesn't matter if you have gained, nobody is there to judge. In fact, you might completely surprise yourself, and the result may not be half as bad as you expected! The important thing is that you go to group, find out how you did and draw a line under it. Sunday is a new week and a fresh start.
You can do this, just believe in yourself and the plan and you'll get there!
Hope that you're feeling better soon. Big hugs xx