Don't be ashamed if spelling isn't one of your talents. There are many, many people out there who aren't strong spellers.
One idea you can do when writing your mystery shop report is to type it out on Microsoft Word first. With this program, it allows you to check for spelling and grammatical errors while you are typing.
This way you can get all of the problems hammered out. Once done, copy and paste what you need and when you need it.
You can easily transfer everything over from Word to your report form, error free!
I know this may sound tedious, but read and re-read your report before you hit the submit button.
Another problem area that gets reports rejected is it wasn't proofread before submission.
If you write a report and leave words out, that's like leaving the punchline out of a joke. You create work for the coordinator because now they have to re-contact you to fill in the gaps. This will cost you points on your overall score for the report.
It realistically will only take you another five minutes to just read your report over a couple times and make sure there are no errors.
Articulate report writing is essential for the coordinator to relay your experiences to the client.
There are many other people wanting to do mystery shops. If you can't write a decent report, those other people will be accepted over you in a heartbeat.