The Prophet (ﷺ) taught this dua to stay safe from Shirk:
اَللَّهُمَّ إِنَّا نَعُوذُ بِكَ مِنْ أَنْ نُشْرِكَ بِكَ شَيْئًا نَعْلَمُهُ وَنَسْتَغْفِرُكَ لِمَا لَا نَعْلَمُهُ
Transliteration
Allaahumma inna nau'dhu bika min an nushrika bika shay'an na'lamuhu wa nastaghfiruka lima laa na'lamuh
Translation
O Allah, We seek refuge in You from ascribing any partner to you knowingly. We also seek your forgiveness from unknowingly [ascribing partners to you].
Allāhumma innī a'ūdhu bika an ushrika bika wa anā a'lam, wa astaghfiruka limā lā a'lam. This masnun dua asks Allah to guard your faith from shirk - whether you know or do not know - and keeps tawheed strong.
First, feel sorry for the sin. Say your Shahadah again. Promise never to do it again. Then ask forgiveness with duas like astaghfirullah. Learning tawheed and praying Islamic dua regularly helps prevent shirk.
Read Surah Al-Falaq and Surah An-Naas for safety from jinn and bad things. Āyat al-Kursī also has great power. It talks about how great Allah is and brings calm to your heart.
A'ūdhu bikalimāti-llāhit-tāmmāti min sharri mā khalaq is very powerful. It asks Allah to shield you from all harm. Say it three times morning and evening for peace and protection, as taught in Islamic prayers.
Study tawheed and keep your actions only for Allah. Make dua asking safety from shirk. Do not show off. Learn Islam from trusted teachers. Say masnun duas regularly and ask Allah to forgive you.