No, I'm afraid it wouldn't.
Pronouns in Greek can be a really hard hurdle to get over my advice is to check out the Tips ¬es first:
See these explanations given by D_.. to other questions::
And my best advice is to try to always use the Drop Down hints (use the top hint) Try to get used to them so you hear which sounds right eventually.
I hope this has been some help please feel free to ask anything if you need to.
"I will make myself a sandwich" is the best translation. I don't see why it wouldn't be accepted, unless there was some other typo in your answer, or a different structure. :/ The answer with in is incorrect. No preposition is needed here.
SInce we can't know for sure what your answer was, if the problem remains, write a comment with a screenshot of your marked answer attached, so we can see it and report the sentence, if there is a bug. ^.^