No, there is no problem steeping your grains loose. That is how you steep (Sacrification) All Grain batches. I make the assumption that you are doing a Partial Mash (PM). The grain bill in a PM is small enough that there should not be any problem. However, it would be a lot easier if you had a bag. You can go to any hardware store and pick up a 1 or 5 Gallon Nylon Paint strainer that will do the job more efficiently than a grain sock, and its reusable. I use them for Hops additions also.
Cheers
Preston