How to adjust the width of a field?

I have achieved what I needed to achieve, however the field which has the PayPal amount is too small and I am unable to make it bigger - is there a way to do this?

Here is the form:

https://form.jotform.co/62491503716859

I checked your form and noticed the same thing. I'm assuming you're referring to this:

(the width is indeed quite small)

To adjust the width, you'd have to inject some lines of CSS codes. Please try the following codes:

#input_15_donation {

   width: 100px;

}

I'm seeing you already have some custom CSS codes added but just in case you'd need guidance on where to put these, here you go:

I have set the width to match the size of the "Amount you wish to pay" field. The result:

Give it a whirl and let us know how it goes :)