BBT question

I took my temp (with a bbt thermometer) this morning first thing before moving... and I got 98.6. I've been around 97.0 for days. This seemed high to me, so I didn't move and went back to sleep for like maybe 15 minutes without the blanket. Took it again and it was 97.0.

Does sleeping with a blanket/comforter really make that big of a difference? I'm concerned I'm not getting accurate results.

I have my thermometer on my side table and literally just move my arm to get it.