"Lest I be, in my invocation of my Lord, unprosperous," meaning: I hope that I shall be prosperous through Him.
﴿عَسَى أَلَّا أَكُونَ بِدُعَاءِ رَبِّي شقيا﴾ أَيْ: عَسَى أَنْ أَسْعَدَ بِهِ