It's harder if you're expecting to receive awards to work at a lab you're already a part of. You may be happy at your lab (and if it's really a good situation for you, I encourage you to keep at it), but there are other opportunities you may be interested in that would have you rotate through other labs temporarily. Your PI should openly encourage you to participate in these, because they allow you the opportunity to affiliate with other institutions which may offer some special admissions consideration for participating.
Last I heard, changes to federal science funding may have impacted these programs, but it is worth doing your own research.
SURF/SURP places students in a lab for a couple weeks over summer and there are usually opportunities to present a poster at the end.
NSF-REUs are also hosted at a lot of different universities across the country in specific areas of study.
NIH-RISE may be offered by your university and is usually a direct research award that could be applied to your current lab if I remember correctly.
You can also look up NIH-MARC, SROP, SIP, IRTA, etc as far as programs intended specifically to help you gain admission to professional school. There are private companies who offer experiences or funding (Amgen Scholars comes to mind).
Hopefully you are early enough in your undergrad career that you can prepare to apply and find success through one or more of these pathways. I really wished I would have had the information when I was going through it.