My Download Keeps Going Back Down?

Okay, so I bought the Sims 4 (I have a Mac) the other day and immediately started downloading it. Everything was going great until it got to about 70%, and then it started going down. Like, today it loaded all the way to 90%, and now it has gone all the way back down to 76%. It's really starting to irritate me and I'm kind of worried it's never going to download completely. Is there any way to fix this, or will it eventually just download on its own?