The past tense of forget is forgot: "I forgot to turn off the stove." The past participle is forgotten or forgot: "You seem to have forgotten (or forgot) me recently." Forgotten is more widely used than forgot as the past participle, but both forms are acceptable. The past-tense form forgat is archaic. Misremember is an archaic or dialectal synonym for forget and should never be used except, possibly, for humorous effect. See also disremember.
Dictionary of problem words and expressions. Harry Shaw. 1975.