You mentioned that you are using PLA and are heating the bed. I have found that with PLA, the first few layers, maybe 1/8" to 1/4" will shrink with a heated bed.

So, I've been coating my bed with the blue removable tape, and not heating the bed. The PLA sticks well enough to the blue tape, and I like that it adds a layer of protection between the extruder and the bed, and between the knife I use to pry off the print and the bed.

With ABS, I heat the bed.