on the surface, three hundred fields sounds like a lot, but it depends on the data involved, Does every product have one and only one entry in every column? if so, then your table is fine. if not you need to break it down.
if you are merging 3 different databases, i'm betting that there will be some fields that are exclusively going to be used by certain product types, those need to be in different tables.
You might want to get a intro to database design book as well.