In case of the doubt between four of five Rak'ats,nyou should take it as four and recite Tashahhud and Salam, then perform two Sajda of Sahw. There no Salat al-Ehtiyat in this case.
Wassalam.
Sayyed Mohammad al-Musawi is originally from Iraq and heads up the World Ahlul Bayt Islamic League in London. Other than being involved in various humanitarian projects, he frequently responds to religious questions. In the past, he has also spent significant time in India guiding the community.