typo: ごちそう, not ごうちそう
先週金曜日に is not wrong, but I would use 先日は unless there is a specific reason to identify the exact date.
社長様に in unnecessary since it's obvious that you are referring to the addressee. It's common to avoid referring to "you" in Japanese. Also note that 社長様 sounds odd when you are talking directly to them.
ごちそうになってありがとうございます is not grammatically wrong, but ごちそうになり is more preferable since -masu stem sounds more formal, and therefore it's more appropriate for your situation. -Te form is acceptable when you use polite forms, i.e., ごちそうになりまして. If you've already learned honorific expressions, ごちそうしていただきまして is the best.
ありがとうございます is not wrong, but the past form sounds more natural.
In conclusion, I would say;
先日は（おいしいお食事を）ご馳走していただきまして、ありがとうございました。