Hey spOOky, my condolences to you and family on the passing of your Grandfather. I see by your location in Canada that you might be Canadian. I suppose that an observance of Canadian custom, tradition or rules would prove your more prudent choice of Kilt / tartan and accessorizing. A swatch of tartan is by no means a full kilt being worn. In the case of grievances the size of the swatch (not yards as in kilt capable) is less relevant and ought be displayed as proudly as one would just as if there were to be an award given just for having it.
Now, since it's a funeral and/or memorial service I think the kilt wearer will be regarded as one simply honoring another in that particular manner. Everyone elses opinion of your wear in your hours of grievance and giving honorable respects is not relevant anyway