It's not about misunderstanding.Gojou you fuck don't fuck this up
Please be a fake-out, I'd hate for this to turn into an arc where they grow apart because he misunderstands her and thinks she's just interested in cosplay, instead of cosplaying with him.
Gojo is trying to see whether he can actually fit inside Marin's life, but because both of them are so far apart in character, he feels that he is holding her back or doesn't belong with her.
And whether Marin rejects or accepts the offer, it is going to affect their relationship. Since Gojo would feel that he is holding her back, if she rejects. And, the chance of Gojo being able to work with Marin would reduce if she accepts the offer.