When God promised You something,He will definitely do it.
What if I sin?
REPENT. God gave us Jesus Christ as a mediator and saviour. He always forgives.
What if I see that Promise is impossible?
Nothing is too small nor too big for Christ. Nothing is impossible. He is so wise that we can’t fathom why it happened.
No one can shut the door God has opened for you. Stop searching for another for yours is open already.
God gave to Joshua the land of Jericho and commanded to keep away from devoted things but Achan didn’t obey. God got angry to His people but gave them another chance (although He still punished Achan). When they went to Ai (for The Lord delivered Ai into the hands of the Israelites) they nearly lost but God is always faithful to His promise and gave His people the victory. He will always find a way.