Are the righteous deeds and prayers of the questioner considered to have been in vain after he uttered the two declarations of faith (Shahadatayn) to appease his mother, who considered his statement "I am an infidel" to be an apostasy from Islam, knowing that he did not intend disbelief?

If the intent of the word was to wear the clothing of disbelievers, and not disbelief that expels one from the religion, then we hope that you do not exit the religion by that. However, if the intent was disbelief, then whoever informs about himself in that manner becomes an apostate. In all cases, if you repent to Allah, He accepts your repentance and restores your good deeds to you, for the one who repents from a sin is like one who has no sin.