Is there not a contradiction between creating man to worship God and creating him for tribulation?

There is no contradiction between man's creation for worship and his creation for tribulation. Worship itself is a test from Allah to discern who obeys Him and who disobeys Him. Tribulation is a test that encompasses all aspects of human life, not just calamities, so that Allah may see how man behaves in all his states – with gratitude or ingratitude, with patience or impatience.

Thus, tribulation is the comprehensive test under which worship falls, as Allah states: (He who created death and life to test you [as to] which of you is best in deed) [Al-Mulk/2], and His saying: (And I did not create the jinn and mankind except to worship Me) [Adh-Dhariyat/56].

Ibn al-Qayyim and Al-Shanqeeti have clarified that the meaning of "to worship Me" is "that I command them to worship Me and test them." The purpose of creation is tribulation and recompense for deeds.