when birthmarks change over time many parents worry that it is a sign that it represents something worrisome. in this case however you are describing a very common (and very normal) hemangioma often referred to as a strawberry hemangioma because of the raised appearance. the changes that you've already noted - going from spotty to more filled in to actually raised are all normal. you can expect for it to grow in size for up to the first 12-18 months of life and then they naturally start involuting or going away on their own. even though they grow initially they eventually go away to the point that at some point during early childhood you will no longer be able to see it at all. imagine that - a vanishing birthmark!
my daughter was born with a bright red birthmark on her back. it is now solid & welted above the skin. should i worry?