"I was not going to say that."
Translation:Ní raibh mé chun é sin a rá.
No. Nílim is the present tense ("I am not"). Ní raibh mé is the past tense ("I was not").
The verb bí is an irregular verb, and the past tense and the present tense don't look like one another, and the negative and interrogative forms are also different from the direct form, so you have tá - an bhfuil - níl in the present tense, and bhí - an raibh - ní raibh in the past tense.
an bhfuil and níl are closer than they seem, as níl is derived from ní fhuil (but it is only written and spoken as níl, never ní fhuil).