Can i still do a 2018 Roth IRA contribution ON tax day April 15th, 2019 or did it need to be done prior? Thanks in advance.

Ask the IRA custodian if they will post it on 4/15 as a 2018 contribution or not.  Many IRA custodians have rules that say they have 3-4 business days to post a IRA contribution that will make it a 2019 contribution.

Yes, you can still make a Roth contribution for 2018 through April 15th, 2019.