:salam:
See this hadeeth:
حَدَّثَنَا هِشَامُ بْنُ عَمَّارٍ، حَدَّثَنَا حَاتِمُ بْنُ إِسْمَاعِيلَ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ حَبِيبِ بْنِ أَرْدَكَ، حَدَّثَنَا عَطَاءُ بْنُ أَبِي رَبَاحٍ، عَنْ يُوسُفَ بْنِ مَاهَكَ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " ثَلاَثٌ جِدُّهُنَّ جِدٌّ وَهَزْلُهُنَّ جِدٌّ النِّكَاحُ وَالطَّلاَقُ وَالرَّجْعَةُ "
It was narrated from Abu Hurairah that:
The Messenger of Allah :saws: said: "There are three matters in which seriousness is serious and joking is serious: marriage, divorce and taking back (one's wife). " (Hasan)
Sunan Ibn Maajah
English reference : Vol. 3, Book 10, Hadith 2039
Arabic reference : Book 10, Hadith 2117
http://www.sunnah.com/urn/1263580
An alternative translation I have seen, is "There are three matters when they are done seriously, they are to be taken seriously, and when they are done jokingly, they are to be taken seriously: Nikah, talaaq, and taking back one's divorced wife."
Source for alternative translation: The Fiqh of family, marriage and divorce, published by the American Open University, written by Jamal Zarabozo, 1997.
As mentioned above, you need to consult a local 'aalim or mufti, as we are not 'ulamaa here. They will need to take into account whether a wali was present, and they will know if it makes any difference if the one accepting is joking as compared to the one offering etc. We cannot help you. You must go to them and explain your situation to them, and get an official answer or fatwa from them.