I had to prepare my son for his shloka competition, but it was so hard to find it..
Finally, I managed to find the right sanskrit lyrics, hopefully, they are correct.
शुक्लां वर्धनम् विष्णुं शशिवर्णं चतुर्भुजं ।
प्रसन्नवदनम् ध्यायेत् सर्वविघ्नोपशान्तये ॥
Shuklaam Vardhanam Vishnum Shashivarnam chaturbhujam
prasannavadanam dhyaayet sarvavighnopashaantaye
Hope it helps