Will a slip of the tongue prayer that includes invoking evil upon oneself be answered, and how can one get rid of this problem?

Errors in supplication do not affect it, for what matters is what is in the heart. Mistakes made inadvertently by the tongue are forgiven, as Allah Almighty says: "And there is no blame upon you for that in which you have erred." Allah knows the intention and purpose of the supplicant. The essence of supplication originates from the heart, and the tongue merely follows it. Supplication is permissible in any language, for Allah knows the supplicant's intention even if their tongue is not fluent. What occurs in the soul unintentionally is not answered, as it is merely a forgiven self-thought. So, supplicate to Allah sincerely with your heart, and do not fear what occurs in your heart unintentionally or what your tongue utters without intention.