You would need to know the variety of the seed you sowed, to check, but, usually when you sow shallot seed, you get a single bulb, which is really a banana onion, rather than a shallot - whatever the seed merchants have chosen to call it
Normal onion varieties are Allium cepa, which do produce seed, and can also be grown to produce sets for planting. True shallots, are Allium Aggregatum which reproduces by basal divisions (similar to garlic) which are split and replanted. These varieties only very rarely produce viable seeds.