You can contribute up to the limit of $18,000 between all 401k type accounts per year. With a solo 401k you can "match" yourself from your business up to 25% of business profits. Assuming your other retirement account contributions are below $15000 from other work, you should be able to contribute that no issue.
If you only made 3k for the year, I would make sure you have a roth option in your solo 401k as well.