Kamal

Wa alaikum salam. This fear is a direct trick of the devil to deprive you of the massive reward of leading the congregation.  You do not need to recite long Surahs to be a good Imam. The Prophet (peace be upon him) commanded Imams to keep recitations short and manageable because there are weak, elderly, and busy people behind you. He frequently recited from the Mufassal section of the Quran, which ranges from Surah Qaf (Chapter 50) all the way down to Surah An-Nas (Chapter 114). Making a mistake is not a crime. If you forget a verse, the congregation is there to correct you. If no one corrects you, say Allahu Akbar and transition directly into Ruku. Your prayer and their prayer remain perfectly valid. Start with the shorter Mufassal chapters you have completely mastered to build your confidence. Step up to the front and claim your reward. Do not let fear hold you back from racing to good deeds. Allah knows best.