i cant imagine how difficult it must be for you, but to be a high achiever and to be aiming for those grades, you seem to be doing brilliantly thus far! if you think your eating disorder may impact your grades, dont hesitate to talk to your teachers or your parents/carers. i know that reaching out may seem challenging and potentially scary, but talking about it to trusted people can really help you to build some strategies to help you maintain good grades, whilst looking after yourself at the same time. If you really really dont want to talk to your teachers or carers, then perhaps reach out to some friends, maybe you guys can hold study sessions together, or you can just talk about whats bothering you to them, or take your mind off it completely and go out for the day.
what you are saying does not sound silly by any means, there is nothing for you to feel silly about in the slightest, however, if you do feel that your eating disorder is beginning to have a great impact on your life, then as i said before, you really should reach out to someone- there is no shame asking for help.
well done for everything that you have done for your GCSEs so far, I wish you good luck!