It is not clear why you did not receive the entire $1200 stimulus---unless you owed back child support. Your stimulus check could be seized if you owed child support. If that is the reason, then, no, you will not receive the difference later. You mention having a child with someone else, so it sounds like that could be what happened to your stimulus check.
We do not know the details of how you and the other parent are claiming your child. As far as the IRS is concerned the custodial parent--the one the child lives with or spends at least 183 nights with--is the one who can claim the child as a dependent. If you have a signed form 8332 between you and the other parent, then the custodial parent can still file as Head of Household, get earned income credit and the childcare credit; the non-custodial parent gets the child tax credit. How the IRS will determine which one of you gets the stimulus $ in 2020 remains to be seen.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
