Update app.py

app.py

@@ -577,7 +577,7 @@ else:
     st.write(f"Thank you for taking part in this study! [Click here]({redirect_url}) to complete the study or copy and paste this code back to finish the study: {study_code}")
 
 # Navigation buttons
-if st.session_state.current_index > 0:
+if 0 < st.session_state.current_index < len(st.session_state.data):
     if st.button("Previous"):
         navigate(-1)
 if 0 <= st.session_state.current_index < len(st.session_state.data):