If one is in doubt whether they recited a brachah or not, they do not recite the brachah again, as it is a question of saying the Name of Hashem in vain. If it is a brachah that someone can be motzei you, then you should try to find someone to do so.

However, there are two exceptions to the above halacha. 1) If one is in doubt if they said bircas hamazon after eating enough to satiate themselves, they should recite the entire bircas hamazan. 2) Bircas hatorah is also an exception, and therefore one should have in mind by ahavah raba to be yotzei, and if they did not do this, then they should recite the brachah of אשר בחר בנו.