Cybersecurity for small saas business

I’m hiring some freelancer off Fiverr to help me developing a php website from scratch. The website is finished with all the basic requirements but I’m sure it’s littered with bugs and major security breaches. I’m not a developer but I can crack it with just the simplest cross scripting attacks I can find on YouTube. What are my options here? Should I hire someone to take care of the flaws first or I’m better off to just launch and worry about it later in case it flops?