I'm not a particular fan of 3M Blue Acrylic, largely because of it's short working time (the time between when you squeeze it out of the tube and when it starts to harden). My preferred putty is 3M Spot-n-Glaze Putty. Its working time is two to three times longer than the blue so I have less wastage than with the Blue. Granted, it's a laquer based putty, but with a few common sense precautions (work in a well ventilated area, wear rubber gloves etc) you shouldn't have any problems. And it can be thinned with laquer thinner until it has the consistency of paint and apply it with a paint brush (which can reduce damage to surrounding detail).
As far as shrinkage goes, just about any form of putty will shrink if applied in thick coats. The answer is to apply several thin coats (waiting until the previous coat has dried well). I usually sand between each layer to help reduce the chance of pin holes in the final surface.
Remember, these are my preferences so my recommendation to you is to see if you can find a small tube of 3M Blue Acryl and try it and see if you like it.