What is the status of the gold I’ve mistakenly bought for it involves usury where I have to pay first then I’ll receive the gold later?
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions and all those who follow his footsteps until the Last Day.
All affairs of trade and muamalah are permissible in syara’, however, there are permissible transactions that should be paid attention to which involves ribawi items (items considered as usury items if it doesn’t follow the syara’ guidance) as to not get involved in usury.
Ribawi items is stated in a hadith narrated from ‘Ubadah bin al-Somit RA, where Prophet Muhammad PBUH said:
الذَّهَبُ بالذَّهَبِ، والْفِضَّةُ بالفِضَّةِ، والْبُرُّ بالبُرِّ، والشَّعِيرُ بالشَّعِيرِ، والتَّمْرُ بالتَّمْرِ، والْمِلْحُ بالمِلْحِ، مِثْلًا بمِثْلٍ، سَواءً بسَواءٍ، يَدًا بيَدٍ، فإذا اخْتَلَفَتْ هذِه الأصْنافُ، فَبِيعُوا كيفَ شِئْتُمْ، إذا كانَ يَدًا بيَدٍ
“Gold is to be paid for with gold, silver with silver, wheat with wheat, barley with barley, dates with dates, and salt with salt, the same quantity for the same quantity and equal for equal, hand to hand (i.e. payment being made on the spot). If these classes differ, sell as you wish as long as payment is made on the spot.” 
According to the above hadith, trade of ribawi items such as gold adornments must be made promptly without any delay. The trade must be made on the spot on one occasion, whether the handover is made directly or through an intermediary (a receipt payment is given). It cannot be delayed later than that.
If there is a condition to postpone the payment or handover of the item, it is included under the category of Riba al-Nasiah, which means usury happens due to the postponement of payment. Furthermore, the prohibition is greater when the postponement of payment includes an additional charge. 
According to the above question, we advise that what has happened in the past to be made as a lesson for us. What’s important is that we never repeat the matter in the future. Repent and supplicate for Allah SWT’s forgiveness and guidance. This is as stated in the statement of Allah SWT:
وَأَحَلَّ اللَّهُ الْبَيْعَ وَحَرَّمَ الرِّبَا ۚ فَمَن جَاءَهُ مَوْعِظَةٌ مِّن رَّبِّهِ فَانتَهَىٰ فَلَهُ مَا سَلَفَ وَأَمْرُهُ إِلَى اللَّهِ ۖ وَمَنْ عَادَ فَأُولَٰئِكَ أَصْحَابُ النَّارِ ۖ
“But Allah has permitted trade and has forbidden interest. So whoever has received an admonition from his Lord and desists may have what is past, and his affair rests with Allah. But whoever returns to [dealing in interest or usury] – those are the companions of the Fire; they will abide eternally therein.” 
Likewise, in another statement of Allah SWT:
عَفَا اللَّهُ عَمَّا سَلَفَ ۚ وَمَنْ عَادَ فَيَنتَقِمُ اللَّهُ مِنْهُ ۗ
“Allah has pardoned what is past; but whoever returns [to violation], then Allah will take retribution from him.” 
Always remember the advice of Rasullullah PBUH regarding the grave sin usury is. From Abu Hurairah RA, Rasullullah PBUH said:
اجْتَنِبُوا السَّبْعَ المُوبِقَاتِ» قَالُوا: يَا رَسُولَ اللَّهِ، وَمَا هُنَّ؟ قَالَ: «الشِّرْكُ بِاللَّهِ، وَالسِّحْرُ، وَقَتْلُ النَّفْسِ الَّتِي حَرَّمَ اللَّهُ إِلَّا بِالحَقِّ، وَأَكْلُ الرِّبَا، وَأَكْلُ مَالِ اليَتِيمِ، وَالتَّوَلِّي يَوْمَ الزَّحْفِ، وَقَذْفُ المُحْصَنَاتِ المُؤْمِنَاتِ الغَافِلاَتِ»
“Avoid the seven great destructive sins.” They (the people!) asked, “O Allah’s Apostle! What are they?” He said, “To join partners in worship with Allah; to practice sorcery; to kill the life which Allah has forbidden except for a just cause (according to Islamic law); to eat up usury (Riba), to eat up the property of an orphan; to give one’s back to the enemy and fleeing from the battle-field at the time of fighting and to accuse chaste women who never even think of anything touching chastity and are good believers.” 
Among the ways suggested by scholars is to increase one’s charity especially in matters involving the public benefit of Muslims. WE take this opportunity to advise everyone who wanted to get involved in any type of trade to first learn the basics of religion as to not get involved in usury. So true is the advice of Umar RA:
لَا يَبِيعُ فِى سُوقِنَا هَذَا إِلَّا مَنْ تَفَقَّهَ فِى الدِّينِ
“No one should sell in our markets except one who has understanding in the religion.”