Unlike many other services, Discord allows multiple users to share the same username. There are two parts of a Discord ID: the username (yours is Rebeccabe) and the discriminator (yours is apparently #0160). There is nothing you can do about this; you must simply give out your full Discord ID Rebeccabe#0160.

For what it's worth, I consider this a rather confusing design flaw in Discord, but I guess they valued the ability for people to have the precise username they wanted. Personally I think it just complicates things.