Recording Coming in Delayed

Audacity 2.2.1
Windows 10 64 Bit
Using an Audio Technica Condenser Mic to record my vocals, it’s plugged into my DBX 286S preamp through the mic input with an XLR. I used a 1/4” Mono to connect the Line output of the preamp to my Focusbrite Solo, and I’ve tried this two different ways. I’ve used a 1/4” Mono to XLR that plugged into the Focusbrite’s mic input, and I’ve tried using a 1/4” Mono to plug it into the “line input” (it was used for instrument but you can change it to line). When I record without any MP3 instrumental it sounds good, I can hear that the preamp is working and the vocals sound clean and crisp. When I try to record with an instrumental track (mp3 ((stereo))file) that runs into my direct monitor so that I can rap on beat, it sounds fine through my headset. But when I play it back it is delayed and sounds like shit, not on beat and not the same rhythm I recorded it in. Please help me out, what am I doing wrong?

You need to correct for latency, see … Latency Test - Audacity Manual

You can correct for Recording Latency. Are you sure the rhythm is off, too? That’s much more serious. Can you tell if the new track is shorter or plays at higher pitch than the backing track? That’s a machine speed problem. A machine that can’t keep up will make a faster track at higher pitch.

You can correct for Recording Latency in post production. Use the Time Shift Tool (two sideways black arrows) and shove the new track sideways until it lines up. If you can get the beginning to line up without the end, that’s a serious problem