Is saying "Masha'Allah, there is no power except by Allah" once sufficient to protect all blessings from the evil eye, and what if I recall another blessing after a short while, should I repeat it, and with what intention should it be said to protect all blessings from the evil eye?

The saying "Ma sha Allah, la quwwata illa billah" (What Allah wills [has come to pass]; there is no power except with Allah) when seeing something admirable, is derived from verse 39 of Surat Al-Kahf. It is an encouragement to praise Allah for His blessings. One can also add a supplication for blessings, such as "Allahumma barik" (O Allah, bless it). Excessive fear of harm and preoccupation with averting it is blameworthy panic and contradicts reliance on Allah. The treatment for obsessive thoughts is to turn away from them and engage in beneficial activities. Morning and evening remembrances, such as "Bismillahil-ladhi la yadurru ma'ismihi shay'un..." (In the name of Allah, with whose Name nothing on earth or in the heavens can cause harm...) and the supplication "Allahumma inni as'alukal-'afiyata fid-dunya wal-akhirah..." (O Allah, I ask You for well-being in this world and the Hereafter...) protect the Muslim. If the obsessive thoughts persist, it is advisable to consult a psychiatrist.