This is due to the fact that order quantity in your order details page is rounded to 3 decimal places.
Here's an example of what you might see. With the quantity showing as '0.033' on the order details page, it may seem that the purchase value is only 0.033 x $2,978.46 = $98.29.
In reality, the quantity purchased is $100/$2,978.46 = 0.0335744, however, this figure is rounded to 3 decimal places (0.033) in the app.
Rest assured that the full dollar amount you've entered has been used to purchase your security.
To check the overall unit quantity that you own in 9 decimal places, kindly click on the Portfolio tab (bottom right corner of the app) > choose the security that you wish to see > click on 'History' button.