Partition won't back to actually size

keg55 is right: if you insist in erasing form the same source you'll probably get the same wrong Recovery Disk.

Boot and install from the net:

https://support.apple.com/en-md/HT204904

(read on top of page for the Mac OS version you want):

- OPTION-COMMAND-R

or

- SHIFT-OPTION-COMMAND-R

depending on you needings.

Wow! I don't know how you created a 303.4GB Recovery HD. That should only be 250MB.

I would suggest you back up your system.

Restart using Command+Option+R (Internet Recovery which will install the current version of an OS your Mac supports - e.g. 10.13.3)

Launch Disk Utility and select your ST3500418AS Media. Click the Erase button to reformat and recreate a single volume (partition) using Mac OS Extended (Journaled) with the GUID Partition Map Scheme.

Then, reinstall macOS High Sierra and during Setup, migrate all your user accounts, data, setttings, apps, etc. from your back up.

You need to use an external recovery to be able to manipulate your drive.

You can't use Recovery Mode (Command+R) to do what you need to do. So, you have to use an external source like Internet Recovery or a clone that you can boot from. Something other than your internal drive which contains your Recovery HD.

I'm done. You're getting conflicting information from me and majortom1967. So, work with him. Good Luck!

I believe you'll get the same result... sorry. You can clone your disk on an external disk and reclone back (Carbon Copy Cloner) but I believe you'll still get a huge Recovery Partition as CCC rely's on the original. Better get an 8 Gbyte USB key and make a Mac OS bootable disk with Disk Maker X. Or a friend that has a clean install of HS (unlikely)

Almost sure. The 32 Gbyte is OK (8 Gbyte or more i required). You need to download HS's installer App once again from App Store. It will be placed into the Application Folder. Disk Maker X should detect it automatically and ask if you want to place it on the 32Gbte key. Go on (it takes a while).

Maybe you need to reformat it.

Please provide a screen shot of Disk Utility so we can see how your drive is partitioned.

Also please provide a the output from this Terminal command: diskutil list

Sorry, I don't see a screen shot posted here.

Please, select Macintosh HD from the finder and get the info window (COMMAND+I) and post the image.

Tnx