I have yet to make a perfect quilt. If the offsets are less than 1/4 inch you should be able to ease them to fit. Pin the intersections and see which blocks are bigger. Put the bigger block next to the feed dogs when sewing and the feed dogs will ease in some of the fullness.
If the block intersections are more than 1/4 inch you either have to decide if you can live with it or figure out if it can be altered. You can trim down your blocks but be careful that the trimming doesn't cut off the points (if you have points) For a first quilt, I would think being done so you can enjoy it will be better than perfect.