What's the difference between an Environmental Engineer and an Environmental Scientist?

Depends on what you get your degree in that makes the difference.  Pay is about the same, but you might get a little more at the start as an engineer, depending on the situation.  It is generally a little easier to get started as an engineer, because there are a lot of peripheral activities in the environmental sector that are more like civil engineering, in very general terms.

What really matters is your ability to observe, think, organize, and write.  That is what you spend a lot of time doing.  If you have trouble in any of these skills, you will likely not succeed.  They are learnable skills, fortunately.