Implantation Bleeding

So last night around 8:30 I went to the bathroom and had bright red blood. This morning when I woke up there was still some bleeding but it was more of a dark/brownish color. I just went to the restroom again and now it's a creamy almost barely brown color. I'm 6DPO and 21CD. My period is like clock work with 28 day cycles. 28 days from the beginning of my period would put me at this Wednesday for a start day. This app doesn't have my period starting until 8/26. So if I don't bleed again like a period bleed when should I test? We are going out of town on 8/31 and I don't want to go without knowing but don't want a BFN if I test too early!