Using dfittool to plot frequency distributions with different lengths boundaries

I have been provided with the following response times in a psychological trial:

Time Frequency

0-0.5 2

0.5-1 14

1-2 50

2-4 20

4-8 7

8-14 1

I need to fit these to a gamma distribution so using dfittool I input [0.5;1;2;4;8;14] as my data and [2;14;50;20;7;1] as my frequency but the density values were in the wrong place and the boundaries didn't connect. Please help