To Be That's the Purpose
There is a distinction Philosophers Blur. If by "purpose" you mean a cosmic intention, a final goal built into the universe by some designer, then neither evolution nor science provides evidence for that. But if by "purpose" you mean the observable direction of living systems, then your argument becomes much stronger.
Life does seem to have a characteristic tendency. Organisms persist, repair themselves, acquire energy, reproduce, avoid destruction, and project themselves into the future. A bacterium does it. A tree does it. A wolf does it. A human does it. In that sense, there is a real directionality. Not a cosmic purpose imposed from above, but an intrinsic tendency of living systems to continue. Evolution does not have a purpose in the sense of a conscious plan. Evolution is not trying to do anything. But evolution produces organisms whose behavior is organized around continuation.
That is something we can actually observe. From your perspective, then, it is perfectly reasonable to say: "My purpose is to continue living and participating in the continuation of life." Notice how different this is from saying: "My purpose is to fulfill the cosmic plan of the universe." The first statement refers to observable biological reality. The second refers to a metaphysical claim. Spinoza might actually be more sympathetic to the first statement than many people realize. He argued that every thing strives to persevere in its being. He called this conatus. A stone persists as a stone. A tree persists as a tree. A human persists as a human. The striving to continue is not a defect. It is the very expression of what a thing is.