All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
Whoever forgets to recite chapter Al-Faatihah (i.e. the opening chapter of the Quran) and begins to recite another chapter, then he should stop reciting the chapter as soon as he remembers and recite chapter Al-Faatihah first, then he may recite any other portion from the Quran after it. What one recites before reciting chapter Al-Faatihah is not considered because it was not recited in its proper place; however, he is not obliged to prostrate for forgetfulness but it is good if he does so.
As regards performing a supererogatory prayer without the Iqaamah, then you should know that no Athaan (i.e. call for the prayer) or Iqaamah is legislated for a supererogatory prayer, rather the scholars stated that it is disliked to call the Athaan and the Iqaamah for a prayer other than the five obligatory prayers, as it is only for obligatory prayers that the Athaan and the Iqaamah are legislated.
Whoever performs an obligatory prayer without saying the Iqaamah, his prayer is valid and he is not obliged to make it up. Saying the Iqaamah is not a condition for the validity of the prayer, but it is disliked to abandon it.
The evidence that the Iqaamah is a Sunnah and that the prayer is valid without it is the narration in which the Prophet was ordering the person who did not know how to pray telling him 'do so and do so' but he did not mention the Athaan or the Iqaamah, while he mentioned ablution, facing the direction of the Qiblah, and the pillars of the prayer, and had the Iqaamah been an obligation in the prayer, he would have mentioned it.
For more benefit, please refer to Fataawa 83388 and 84204.
Allaah Knows best.