There are a few reasons why you might see a different amount in you bank account from what you initially saw in the Instawork app.
Adjustments - after you work a shift, our clients will typically send us a timesheet for the hours you worked. So while your shift, for example, might have been booked for 1-5pm, the timesheet might show you worked from 1:10-4:58pm. In this case, you'll get paid the actual amount our client tells us you worked.
Taxes - if you're a W2 pro, Instawork deducts taxes from your pay automatically. You'll receive weekly paystubs which will reflect the deductions from your earnings and you can access this in ADP. You can learn how to do that here: https://help.instawork.com/en/articles/3840040-how-to-view-your-w2-paystubs.