Sorry to ask - thought i'd give it one more try!

What do the experts recommend as a width for sealant around a bath. I've been putting this job off for weeks now as the last time I attempted it, it looked as Stevie Wonder had put the Silicone down.

How wide should the gap be between the two bits of masking tape (thanks for the tip on an earlier post)???. I cant delay any longer, 'er indoors wants to know why we still cant use the bath.......I'd be really grateful for more expert advice - my wet finger has a date with some silicone and I cant delay any more!
Thanks
Alex