Did you measure it yourself? Is the fabric really 10.5' long? Many - if not all... - of these brands claim 10.5' only to add in the small print that the length is measured from hook to hook. However, the only length that is important is the one of the fabric; or rather from gathering point to gathering point. My guess is, that your hammock is 9.5' x 6.5'. Unfortunately, you can only use that kind of width if the hammock is much longer. The shorter the hammock, the more pronounced the bathtub shape becomes.

If you're not afraid to sew, you could simply remove one or even both of the side panels. Also, forget the 30° angle and 83% ridgeline "rules". They're just starting points for 11' hammocks. If the hammock is longer, a steeper angle / shorter ridgeline might be more comfortable. If the hammock is shorter, a shallower angle / longer ridgeline might be more comfortable. Just play around with these parameters and find the right settings for YOU and THIS specific hammock.