Check out university-specific job system postings before you take on free labor opportunities. Depending on the university, some offer full-time or part-time paid research assistant positions that are perfect for a fresh Bachelor's alum, plus you'll also get to earn some or all of your living while doing it. Paid opportunities also often mean more important research experiences because you may be expected to do a lot more beyond what a typical undergrad volunteer RA would be doing (e.g., scoring protocols).
Also, be flexible about the actual research questions you're involved in if the opportunity would offer you research experience that would be applicable to your ultimate research goals. For example, say your "dream study" includes conducting fMRI studies with ASD participants in the future as a Ph.D. or doctoral student. Research work in a neuroimaging lab that includes fMRI studies about non-ASD people and getting some experience with fMRIs or writing grants for this work would go farther for you than RA work in an ASD lab that just involves you scoring protocols. Seek important less topic-related research opportunities over topic-related but unimportant opportunities. I helped write IRB and grant proposals for a deaf and hard-of-hearing study as an undergrad. I (and future POIs) had zero interest in deaf or hard-of-hearing as a research topic, but my experience with the proposals looked very attractive to future POIs when applying for grad school.
As
@singasongofjoy indicated, master's degrees cost money AND don't guarantee research opportunities any better than volunteer research opportunities, which at least are free to perform, even if they don't net you money. If you know you're going for a research-focused Ph.D., then don't waste time on a master's degree before applying, because most psych fields are not expecting or desiring this from incoming doctoral applicants anyway.