Almost tripled in size on 2nd day??

Hi all!

I am new to this sub and this is my starter I named Harriet that I started from scratch. This is a pic from last night when she was on her second day. I have been feeding her in the morning with just unbleached APF and filtered water at a 1:1:1 ratio with slightly less water cause I’ve heard keeping the starter thicker is better overall. I’m assuming this is a false rise from the research I’ve done, but is this normal for only 2 days? She wasn’t rising much at all until I added this heating mat in her area since my house is so cold. This morning when I went to feed her she had only sank down slightly from where she’s at in this pic, probably right under the label. I forgot to take a pic for reference lol

I just want to see if anyone else has had this happen and reassure me that I’m doing this right :) any tips n tricks are very appreciated!