Will I be sinful for delaying the marriage contract with my fiancée for over a year and three months due to my inability to raise the marriage funds, and what should I do if I am sinful?

There is no sin upon you for delaying marriage due to financial hardship and gathering expenses, as this is a valid excuse. You should seek their permission and inform them of your real need for time to gather the provisions. If they permit, then there is no harm. It is recommended to facilitate marriage, ease the dowry, and reduce its costs.