Swatching frustration

Knitting up swatches is painless. Yes, a little tedious when all you want to do is dive in and start knitting your project, but look at these two swatches:

I made these two swatches with the same amount of rows and the same amount of stitches. Only difference is the top swatch was made with size 7 addi circulars and the bottom swatch is with size 8 addi circulars. There's a HUGE difference!!!

My pattern calls for 18 stitches & 26 rows in St st = 4" on size 7's. The swatches totally tell me I'm a tight knitter. My gauge was pretty off. I had too many stitches/inch using 7's so I felt that going up to size 8's would be better. I'm still a little off but it's better than 7's. I dunno...I think I know what I'm doing and maybe I'm figuring my gauge wrong. I'm going to start knitting Wicked and my gut feeling is telling me it's ok to use size 8's and not have an anxiety attack if it doesn't work. I also like how the size 8 swatch feels...it's drapey just like the sweater should be. I can always start over, get some help at an LYS, and get on with it. I know it's only yarn, but it's my first sweater. I'd like to do it right the first time without crying. Uh oh. Maybe this is a bad week to start this. PMS is going to hit soon.