مبطلات الصلاة

A prayer is spoiled by: breaking wudu, speaking on purpose, eating or drinking, turning away from the qibla without need, laughing out loud, and many unnecessary movements. Forgetting is forgiven: if you add or miss a part by mistake, you can often repair it with two prostrations of forgetfulness (sujud as-sahw) before or after the salam, as the Prophet ﷺ did (reported by Bukhari and Muslim).

When you are unsure how many rak'ahs you prayed, you build on the number you are sure of. Do not panic: a calm prayer matters more than a perfect memory. Schools of law differ on some details: follow your family's and mosque's school, and ask a teacher.