Start samples in Garageband

[Redw28]

I am using an M-Audio Axiom Air Mini 32 and Garageband 10.3.3 for Mac. I can assign samples to the keyboard but I have to keep the key or pad pressed to allow it to keep running. I want to hit allocate different samples to pads, hit one to start the sample, then while that is playing I can play something else on keyboard or guitar. Sounds like something I should be able to do but I just can't work it out.

Thanks for the help.

Pete