Jpeg saving too small

I think I have been working too small, but I can't figure out how to fix it. 

I work on a canvas that is 30x30inches (3000x3000 pixels) but my images are saving out too small, I need them to be at least 1mb . 

Everything I've looked up says that my canvas should be PLENTY big enough to save out 1MB images but they're not even close, coming out as 100kb or smaller. 

How do I fix this? What is the right size? 

All the questions I've seen so far people seem to be having the opposite of my problem!