Congrats on beginning your first quilt!
One idea is to match up the middle seams and cut off the extra fabric on each side so that all the block pairs are now equal sized.
The other idea is to introduce yourself to your seam ripper. I have a long standing love-hate relationship with mine - he's like family. :D
I agree with Maride that 1/4" seams are easier to handle. A 1/4" foot can be purchased at any hobby store, even Walmart, for about $5-$7. It's such a simple thing that makes a world of difference.
Also, if you can post a picture of what your blocks look like, we'll probably be able to give you better feedback on how to fix it.